The deformation modes are investigated which develop in the critical regions of reinforced concrete (R/C) walls subjected to inelastic cyclic loading. A general method for wall design against shear failure, in particular sliding shear failure that occurs at high ductility levels, is suggested. This method of estimating sliding shear strength takes into account the presence or not of bidiagonal reinforcement at the critical area of R/C walls. Proposed models are compared with experimental results, as well as code provisions. Some open questions regarding wall design and detailing are addressed. An analytical approach for predicting the magnitude of displacement components of R/C wall specimens is also presented. Examples of application of this methodology in wall specimens tested to failure are then presented. Measurements of purposely located elongation meters (LVDTs) are used for the application of the proposed methodology. Conclusions are drawn regarding the breakdown of total horizontal displacement into flexural, shear and sliding shear components at each displacement-ductility level. Diagrams resulting from the application of this methodology are also presented, indicating that the sliding shear deformation mechanism becomes critical for shear walls with an aspect ratio between 1.0 and 1.5.
Presented is a detailed case study on structural identification and Finite Element (FE) modeling of a 14-story office building. Specifically, system identification tools were used to identify the structural dynamic properties based on recorded seismic data. This identified model was compared with a model based on IBC 2000 using the fundamental period, design response spectral acceleration, and base shear. The two models were found to be about 20% different in these parameters. Then, a series of three-dimensional FE models were created to study various approaches for improving the accuracy of FE models quantitatively. Sensitivity study shows that the most effective ways to improve the accuracy of linear FE models are to refine the mass calculation and consider the panel zone rigidity of the beam/column connections for this type of structure. Simulated seismic responses were compared with the observed responses and it is found that a FE model can be calibrated to give a good prediction of earthquake response.
Real accelerograms are nowadays an emerging option for defining the input to geotechnical and structural dynamic analyses. A key issue is the selection of appropriate acceleration time-histories since seismic design code recommendations are limited in this respect and also well-established procedures are not available. In the paper a simple approach for selecting and scaling a set of real accelerograms was followed which took into consideration magnitude and distance search windows, record-to-record variability of spectral ordinates with respect to the target spectrum and the prevention of seismic event domination within a set. This procedure was applied to a real case, i.e. the selection of real accelerograms representative of the March 1638 Calabria earthquake that severely struck the historical town of Nicastro (Southern Italy). The selected time-histories represent an appropriate input for the numerical response analyses of the site to adequately evaluate the seismic hazard, which is a fundamental step of seismic risk evaluation.
On Tuesday 17 January, at 5.46 a.m. local time, a 7.2 magnitude [Japan Meteorological Association (JMA) MW6.9] earthquake struck the Kobe-Osaka region of Japan. The region is Japan's second-most populated and industrial area, after Tokyo, with a total population of about 14.1 million. Preliminary estimates are that approximately 5100 deaths have occurred, with about 26000 persons injured, 300000 initially homeless and more than 100 000 buildings badly damaged or destroyed.The loss of life caused by the earthquake is the worst in Japan since the Great Kanto, Tokyo, earthquake of 1923, when about 140 000 people were killed, mostly by the conflagration following that earthquake. The economic loss of the 1995 event may be the largest loss ever caused by a natural disaster in modern times. The direct damage caused by the shaking is estimated at over ¥13 trillion (U.S. $130 billion).This preliminary report provides a brief overview of the event and its implications for engineered structures. The first author was present in Osaka at the time of the earthquake and spent the next 12 days surveying damage, together with the second author and 10 other colleagues from EQE International who arrived shortly following the earthquake.
This paper presents the results of the structural identification of a historical structure damaged during the 17 August 1999 Kocaeli earthquake. Results of the structural models and methods are cross-validated in order to identify the reliable dynamic characteristics. Spectral analysis of the eight structural points yields average peak frequencies, respectively at around 2.5, 3.5, 4.3, 5.3 Hz and so on for NW–SE direction. Similarly for the SW–NE direction, peaks are seen at around 2.6, 3.2, 4.5–5 Hz with small differences in amplitudes between different structural points. Among the stations, station 3 behaves differently than the other observation points in low and high frequency regions indicating that the data recorded at station 3 should be examined in more detail.
A series of two- and three-dimensional static and dynamic inelastic frame analyses are performed for a 17-story steel moment frame building damaged by the 1994 Northridge earthquake. The primary objectives of the study are to: (1) exercise state-of-the-art inelastic static and dynamic analyses for the evaluation and design of steel buildings; (2) establish to what degree frame analyses can be used to predict the types of brittle connection damage that occurred during the Northridge earthquake; and (3) investigate the reliability of the analyses and the influence of modeling parameters on computed performance indices. In general, this study shows that calculated interstory drift ratios and curvature demands obtained from inelastic time history analyses correlate reasonably well with the pattern of connection damage observed in the building. However, there is significant scatter in the computed deformation demands that are strongly dependent on the degree to which three-dimensional torsion, secondary structural elements and strength/stiffness degradation (associated with connection fractures) are modeled in the analyses. Further, comparisons of static and dynamic analyses indicate that for this building static pushover analyses do not capture higher vibration modes that are significant.
In Germany, high-strength concrete was used for the first time for the construction of the 186 m high office building ‘Trianon’ in Frankfurt. As the German standard for reinforced concrete does not cover a strength of 85 MPa, special approval by the relevant state building authority was required. The paper reports on the chosen mix design, design assumptions, fire tests, experience on site, quality control and economic aspects.
A set of fragility curves for the bridges commonly found in the Central and Southeastern United States (CSUS) is presented. Using the results of an inventory analysis of the typical bridges in the CSUS, four typical bridge types are identified. Using nonlinear analytical models, and a suite of synthetic ground motions, analytical fragility curves are developed for the four bridge types. The fragility curves were first generated for the individual components of each of the bridge types and then, they were combined into fragility curves that represent the entire bridge system using first-order reliability principles. The fragility curves show that the peak ground acceleration for a 50% probability of exceeding slight damage ranges from approximately 0.19 to 0.24 g for the four bridge types. Comparison of the fragility curves shows that the most vulnerable bridge types are the multi-span simply supported and multi-span continuous steel-girder bridges. The least vulnerable bridge is the multi-span continuous pre-stressed concrete-girder bridge. The developed fragility curves can be used for economic loss estimation as well as a basis for assigning retrofit prioritization for bridges. This is particularly useful in the Central and Southeastern United States where seismic retrofit of bridges is becoming more prevalent.
This paper presents a survey of building pounding caused by the 1989 Loma Prieta earthquake. Pounding was present over a wide geographical area including the cities of San Francisco, Oakland, Santa Cruz and Watsonville. The survey database contains more than 200 pounding occurrences involving more than 500 building structures. The paper discusses the distribution of pounding damage in the specific areas, types of pounding damage, and examples of pounding damage involving major miltistorey buildings. Some significant pounding occurred at sites with large epicentral distances indicating the possible catastrophic damage that may occur during future earthquakes having closer epicentres.
A large number of steel bridges were damaged by the January 17, 1995, Hyogoken–Nanbu (Kobe, Japan) earthquake. This damage is particularly relevant to Eastern North America where considerably more steel bridges exist than in Western North America where bridges exposed to past earthquakes were mostly of reinforced concrete. Therefore, in light of the Kobe earthquake, a comparison of the steel design practice and design requirements in Japan and North America is instructive. In this paper, such a comparison is first presented, followed by a review of the observed damage to steel bridges and a review of the causes for this damage. Then, the relevance of these observations to North American bridge design practice is examined.
According to the results of the previous inversion studies, the main ruptures of the 1995 Kobe earthquake occurred on two faults, namely the Nojima and Suma faults, which have a step-over about 4 km wide in the Akashi strait. However, the possibility of the rupture in the step-over itself has not been clarified yet due to the unavailability of near-epicentre seismic data. To this unavailability, free-field ground motions at the piers of a suspension bridge located in the step-over are derived from the vibration records of its towers. The ground motions are successfully derived within 0.6–1.2 Hz, where the transfer functions are stable and the influences of the cable vibrations are negligible. The preliminary analysis of the obtained ground motions shows that although the ruptures of the main faults could simulate the early parts of the ground motions, they fail to recover a major pulse afterwards. This suggests that the step-over might have had a delayed rupture.
Described herein are the performances of and damages to steel bridges and viaducts during the Hyogoken-Nanbu earthquake in relation to past design specifications. A particular emphasis is placed on the performance of steel bridge piers and their buckling, low-cycle fatigue and brittle crack failures. Numerical simulation of typical damage such as elephant-foot buckling, failure of bearing devices and dynamic interaction of steel piers from adjacent reinforced concrete piers is carried out and possible causes are discussed. Finally, concluding remarks on the key concepts for earthquake-resistant design of bridges, several recommendations for the improvement of steel pier design and comments on future research needs are made.
On June 27, 1998, an earthquake measuring 5.9 on the Richter scale rocked the Adana–Ceyhan region of Turkey, an important industrialized and agricultural area of about two million population. It resulted in 145 deaths, more than 1,500 injuries and significant damage to more than ten thousand structures. In this paper, the observed structural damages are analyzed in view of the strong ground motion characteristics, the geological conditions and the building codes. Geotechnical aspects such as soil liquefaction and site amplification effects that considerably influenced the damage patterns at many areas are also briefly discussed. It is believed that the information presented herein is important to the engineering community as the observed seismic performance of the structures in this earthquake gives a good indication as to the aseismic strength of the whole Turkish building stock.
In the years 1999 to 2001 a new natural draft cooling tower has been built at the RWE power station at Niederaussem, with 200 m elevation the highest cooling tower world-wide. For many reasons, such structures can not be designed merely as enlargement of smaller ones, on the contrary, it is full of innovative new design elements. The present paper starts with an overview over the tower and a description of its geometry, followed by an elucidation of the conceptual shape optimization. The structural consequences of the flue gas inlets through the shell at a height of 49 m are explained as well as the needs for an advanced high performance concrete for the wall and the fill construction. Further, the design and structural analysis of the tower is described with respect to the German codified safety concept for these structures. Finally, the necessity of extended durability of this tower is commented, the durability design concept is explained in detail and illustrated by virtue of a series of figures.
An earthquake struck the city of Bingöl, Turkey on May 1, 2003. A total of 1351 buildings were heavily damaged or collapsed in the city center and surrounding villages. Recorded ground acceleration was relatively high compared with that of other recent Turkish earthquakes. Its peak value was approximately 5.45 m/s2. Duration of the strong ground motion with large amplitudes was relatively short at approximately 10 s. Ground accelerations and response spectrums for this earthquake are illustrated in this paper. Seismic code requirements are discussed and compared with observed earthquake damage. Many structural deficiencies and mistakes such as nonductile details, soft and weak stories, poor concrete quality, short columns, strong beams–weak columns, large and heavy overhangs and unconfined gable walls were observed.
A field investigation of the 26 December 2004 south east Asia earthquake- and tsunami-affected areas in Thailand and Indonesia was conducted. The objective of the study was to evaluate the effects of the event on buildings, bridges and infrastructure. The effect of the tsunami on structures and infrastructure produced surprising behaviour with several new lessons to learn. Failure of critical infrastructure such as bridges, harbour docks, hospitals and communication systems delayed search and rescue operations and relief efforts, which increased the suffering of the survivors. The causes of structural failures due to the earthquake included soft story, strong beam–weak column designs, short columns, deficient beam–column joints, non-ductile detailing, unreinforced masonry and inadequate construction quality. It is concluded that it is necessary to design critical structures and important infrastructure to survive tsunami effects. Well-designed and constructed structures with attention to details and no significant additional cost survived the earthquake and the resulting tsunami with minimum damage.
The devastating Mw 9.1 Sumatra earthquake on 26 December 2004 and subsequent tsunami caused severe damages to harbour structures which caused delay in supply of relief work in the earthquake and tsunami affected areas in Andaman Islands, India. Major structural damage was observed at the construction joints due to pounding of two portions of jetties and at the top of reinforced concrete piles, especially short piles. Inadequate structural design and reinforcement detailing along with poor maintenance of these structures were primarily responsible for the severe damages. Other geotechnical aspects, e.g. liquefaction of soils, slope-stability failure, etc., were also responsible for severe damage to these structures. Appropriate seismic design provisions in applicable codes and their implementation are necessary to ensure satisfactory structural response for uninterrupted services at harbours in seismically active zones, especially those in developing countries.
On October 8, 2005, an earthquake of magnitude Mw 7.6 shook northern Pakistan particularly the Kashmir region. With nearly 73,000 dead, 70,000 injured, 270,000 buildings destroyed, and 180,000 damaged, the earthquake ranks amongst the worst natural disasters in the history of Pakistan and the Indian subcontinent. In this paper, the shaking intensity distribution of the affected region is reconstructed using the limited ground motion data available. Selection of a suite of records representative of characteristics of the Kashmir earthquake at locations of major damage is undertaken. An ensemble of buildings is collated which represents (i) actual Pakistan reinforced concrete design, (ii) general non-seismic and (iii) code-conforming buildings with different levels of detailing. The buildings are subjected to the selected records, including the vertical component of the earthquake ground motion thought to be significant in this earthquake. Conclusions are drawn with regard to the relative performance of the different types of building investigated, the effect of different levels of design and detailing, and the effect of the vertical earthquake component on damage. It is observed that buildings that are seismically designed to contemporary codes would have survived the earthquake. However, the vertical motion would have caused significant reduction of shear capacity in vertical members. The extensive results reported in the paper are useful for practicing engineers operating in areas of high seismicity where limited seismic design and construction quality control exist, as well as code drafting panels interested in the effect of multi-axial excitation on reinforced concrete buildings.
A devastating earthquake struck the southwestern Chinese province of Sichuan on 12 May 2008, leaving 69,227 dead and 374,643 injured, with 17,923 people still missing five months after the main event. The epicentre of the earthquake was located in Wenchuan County, which triggered a fault rupture length of about 300 km, stretching northeast through Beichuan County and reaching Qingchuan County; many towns on both sides of the fault were severely damaged/destroyed, reaching an earthquake damage intensity of XI. This paper presents the findings of a post-earthquake reconnaissance field mission carried out by the Earthquake Engineering Field Investigation Team (The Institution of Structural Engineers, UK) and by the European Laboratory for Structural Assessment of the Joint Research Centre of the European Commission, through the description of the damage sustained by three of the towns that suffered the largest levels of devastation: Yingxiu Town of Wenchuan County, Beichuan Town of Beichuan County, and Hanwang Town of Shifang City. The work focuses on the description of building performance during and after the disaster, in particular of reinforced concrete frame, reinforced concrete confined masonry, unreinforced and unconfined masonry, industrial, local vernacular and historical buildings. The information and recommendations provided in this paper will be useful for future engineering applications in similar earthquake risk regions.
For rigorous numerical analyses of the behaviour of cooling towers, it is necessary to consider an accurate model which takes into account reinforced concrete behaviour, crack distribution and geometrical imperfections. On the other hand, since these structures are thin shells, the analyses must consider the phenomenon of instability. A 2D modelling based on the Fourier series has been adopted to take into account the above mentioned damage. After an accurate description of the typical damage observed on several cooling towers, the paper presents parametrical analyses of the influence of the different damages on the strength of the structure. Two different loads are successively analysed: (i) self weight; (ii) self weight and wind. The results show the importance of the state of cracking of the shell and of the differential settlement on its strength.
In order to extend the Swiss railway grid in the 1960s and 70s, many railway bridges were constructed for which pot bearings were taken for the supports. It is essential that the long-term behavior of these pot bearings is examined, as their life expectancy is, in most cases, much more limited than that of the associated superstructure. In this study, the operational condition of the pot bearings from a prestressed concrete girder bridge was investigated through in situ measurements and by evaluating the accumulated sliding path due to traffic loads and temperature impacts. It was found that long-term effects in relation to the traffic loads affect minimally the fatigue behavior of the bearings. Within extensive laboratory test series, the influence of parameters such as the lubrication condition, rotation angle, pressure acting on the elastomer pad and temperature on the restoring moments of the pot bearings was studied. Results of this study indicate not only that the condition of the pot bearings has deteriorated, but also that they were still in reasonable working condition after 32 years of service.
This paper presents a hypoplastic model for three-dimensional analysis of concrete structures under monotonic, cyclic, proportional and non-proportional loading. The constitutive model is based on the concept of equivalent uniaxial strains that allow the assumed orthotropic model to be described via three equivalent uniaxial stress–strain curves. The characteristics of these curves are obtained from the ultimate strength surface in the principal stress space based on the Willam–Warnke curve. A cap model is added to consider loading along or near the hydrostatic axis. The equivalent uniaxial curve is based on the Popovics and Saenz models. The post-peak behavior is adjusted to account for the effects of confinement and to describe the change in response from brittle to ductile as the lateral confinement increases. Correlation studies with available experimental tests are presented to demonstrate the model performance. Tests with monotonic loading on specimens under constant lateral confinement are considered first, followed by biaxial and triaxial tests with cyclic loads. The triaxial test example considers non-proportional loading.
This paper presents a method for the integration of a class of plastic-damage material models. The integration of the evolution equations results in a nonlinear problem, which is linearized and solved with the Newton–Raphson method using a sub-stepping strategy. The consistent tangent matrix can be formulated either in terms of the stress components in a general reference system or in terms of the principal stress and strain components with the former then transformed to the general reference system. In order to account for plane stress conditions, the stress–strain relations of the 3d material model are then condensed out. Plane stress conditions are imposed by the linearization of the stresses that need to be set equal to zero; thus the strain fields are updated in the corresponding directions. This solution method is extended to include transverse pressure and the effect of transverse reinforcing steel for a 3d concrete material model. The equilibrium of the stresses in the reinforcing steel and concrete is linearized and the strain fields are updated until the residual satisfies a specified tolerance. The consistent tangent matrix due to the condensation process is derived. The proposed algorithms are tested at the material and element level by comparison of numerical solutions with available experimental data.
This paper presents a model for the analysis of reinforced and prestressed concrete frame elements under combined loading conditions, including axial force, biaxial bending, torsion and biaxial shear force. The proposed model is based on the simple kinematic assumptions of the Timoshenko beam theory and holds for curved three dimensional frame elements with arbitrary cross-section geometry. The control sections of the frame element are subdivided into regions with 1D, 2D and 3D material response. The constitutive material model for reinforced and prestressed concrete follows the basic assumptions of the Modified Compression Field Theory with a tangent-stiffness formulation. The validity of the model is established by comparing its results with several well-known tests from the literature. These simulations include a variety of load combinations under bending, shear and torsion. The analytical results show excellent agreement with experimental data regarding the ultimate strength of the specimen and the local strain response from initiation of cracking to ultimate load.
This paper present a new algorithm of plastic optimization for 3D steel frames under fixed loading (limit optimization) or repeated loading (shakedown optimization). The weights of the frames are minimized under constraints of plastic collapse (instantaneous mechanics/alternating plasticity). A 3D plastic-hinge considering two bending moments and axial force is taken into account by 16-facet polyhedrons. The static theorem of limit analysis is adopted and the formulations are written under a linear programming problem that is solved by using the simplex method. Several useful techniques of reducing the problem sizes are proposed. Some numerical examples are presented to demonstrate the efficiency of the proposed algorithm.
To investigate more precisely the seismic response of interactive soil–pile–structure systems, a three-dimensional finite element subsystem methodology with an advanced plasticity-based constitutive model for soils has been developed. The structure subsystem is represented by space frame elements while the pile–soil subsystem is idealized as an assemblage of solid elements. By means of the δ*-version of the hierarchical single surface (HiSS) modelling approach for cyclic behavior of soft clays, tangent matrices of the soil properties are formulated with distinct constitutive laws for individual stress–strain regimes such as virgin loading, unloading, and reloading. A successive-coupling, incremental solution scheme in the time domain is created to take account of both inertial and kinematic soil–pile–structure interactions simultaneously. The seismic inputs can be any combination of three-dimensional motions. The proposed methodology may be used to analyse the seismic responses of structures for different support excitations such as rigid ground motion, interactive pile-foundation motion, and, for long span structures, non-uniform free-field motion.
The current confidence levels in the ability to provide buildings with adequate resistance to horizontal actions do not easily apply to historic and existing masonry structures. Limit analysis is often not sufficient for a full structural analysis under seismic loads, but it can be profitably used in order to obtain a simple and fast estimation of collapse loads. Often, the limit analysis of ancient masonry structures is used in the context of several simplifications, the assumptions about the collapse mechanisms being the most relevant. Aiming at a more general framework, a micro-mechanical model developed previously by the authors for the limit analysis of isolated in- and out-of-plane loaded masonry walls is extended here and utilized in the presence of coupled membrane and flexural effects. In the model, the elementary cell is subdivided along its thickness in several layers, where fully equilibrated stress fields adopting a polynomial expansion are assumed. The continuity of the stress vector on the interfaces between adjacent sub-domains and anti-periodicity conditions on the boundary surface are further imposed. Linearized homogenized surfaces for masonry in six dimensions are obtained and implemented in a FE limit analysis code, and two 3D case studies are analyzed making use of the kinematic theorem of limit analysis. From the results, the approach proposed is validated and its usefulness for solving engineering problems is demonstrated.
In the paper a numerical procedure is described for the dynamic analysis of seabed anchored floating structures, with particular reference to the so-called Archimedes bridge solution for deep water crossings; attention is devoted to the design solution encompassing slender bars as anchor elements. A geometrically nonlinear finite element, developed in previous work, is here refined extending its capabilities to full 3-D analysis and to nonlinear modelling of hydrodynamic loads due to steady current and wind waves. The element is implemented in a numerical procedure for the dynamic time domain step-by-step analysis of nonlinear discretized systems; consistently, hydrodynamic and seismic loading are introduced by generating artificial time-histories of spatially variable seismic motion and wind waves.An example of on application is shown regarding the behavior of the dynamic model of a submerged tunnel proposed for the Messina Strait crossing. The model is subjected to an extreme multiple-support seismic loading having a PGA equal to 0.64g and to an extreme wave loading with significant wave height of 16 m. The dynamic behaviour in the two loading situations is illustrated and compared, showing interesting facets, especially in terms of interaction between the tunnel and anchoring bars oscillations.
Recent trends towards constructing taller buildings with irregular geometric shapes imply that these structures are potentially more responsive to wind excitation. The wind-induced motion of modern tall buildings is generally found to involve with significant coupled lateral and torsional effects, which are attributed to the asymmetric three-dimensional (3D) mode shapes of these buildings. The 3D coupled modes also complicate the use of high frequency force balance (HFFB) technique in wind tunnel testing for predicting the wind-induced loads and effects on tall buildings. This paper firstly presents the analysis of equivalent static wind loads (ESWLs) on tall buildings with 3D modes provided that the wind tunnel derived aerodynamic wind load spectra are given. Then an integrated wind load updating analysis and optimal stiffness design technique is developed for lateral drift design of tall asymmetric buildings involving coupled lateral–torsional motions. The results of a practical 40-storey building example with significant swaying and torsional effects are presented. Not only is the technique able to produce the most cost efficient element stiffness distribution of the structure satisfying multiple serviceability wind drift design criteria, but a potential benefit of reducing the wind-induced loads can also be achieved by the stiffness design optimization method.
This paper discusses the adaptive approach in genetic algorithms (GAs). It is tried to show how the adaptive approach affects the performance of GAs, suggesting some improvements in both the penalty function, and mutation and crossover. A strategy is also considered for member grouping to reduce the size of the problem. Some practical design of space truss examples taken from technical literature are optimized by the algorithm suggested in the current work. Design constraints such as displacement, tensile stress and stability given by national specifications are incorporated and the results are compared with the ones obtained by previous studies. It is concluded that the member grouping together with the adaptive approach increase the probability of catching the global solution and enhance the performance of GAs.
Guangdong International Building has a height of approximately 200 m with 63 stories. This paper describes some selected results obtained from the full-scale measurements of dynamic behavior of this tall building. The dynamic characteristics of the buildings are determined based on the field measurements and comparisons with those calculated from the computational model of the buildings are made. The amplitude-dependent characteristics of damping obtained by the random decrement technique are presented and discussed. In parallel with the field measurements, a series of wind tunnel tests are conducted to determine the spectral model of across-wind force on rectangular tall buildings with various side and aspect ratios. The wind-induced responses of the building in along-wind and across-wind directions are evaluated by random vibration method based on the established spectral model of across-wind force. The serviceability of this building is discussed in detail on the basis of the computational results.
This paper describes six tests carried out on reinforced concrete (RC) beam to concrete-filled steel tubular (CFST) column planar frames subjected to ISO-834 standard fire. Each frame consists of two CFST columns and an RC beam with RC slab. These tests were meant to reproduce the conditions of the CFST columns and RC beams in multi-storey composite buildings commonly used in Chinese high-rise and subway constructions. The columns in four of the framed specimens used circular steel tubes while the remaining two used square tubes. Other test parameters include the level of axial load in the CFST column, the load level in the RC beam and the beam-to-column linear rotational restraint ratio. Temperature distributions on the composite column sections, beam sections and in the joint zones were measured during the tests. By analysis of the deformations and failures of the test specimens, differences between the fire behaviour of the CFST columns and RC beam members being in a frame and being isolated members are identified and failure mechanisms for the planar frames are proposed. The influences of different testing parameters on the limiting temperature of the planar frames are also discussed.
The role of soil–foundation–structure (SFS) interaction on seismic behavior of an elevated highway bridge (the I-880 viaduct) with deep foundations is investigated in this paper. A series of time domain, inelastic finite element simulations of seismic behavior of a bridge bent subjected to various earthquake events is carried out using two separate models of the system. The first model assumes the bridge columns to be rigidly connected to the foundation without SFS interaction. The second model incorporates SFS interaction through the use of equivalent springs. The spring properties are derived from three-dimensional finite element analysis of the pile foundation in a layered soil system. The analysis is based on nonlinear inelastic characteristics of the concrete substructure and linear elastic behavior of the soil–foundation system, which was determined to be a reasonable assumption for this case study. The ground motions used in the simulation studies describe the expected hazard at the site and represent earthquakes with a 10% probability of being exceeded in 50 years. Results of the analysis indicates that SFS interaction can have both beneficial and detrimental effects on structural behavior and is dependent on the characteristics of the earthquake motion.
AASHTO has specified probability-based design methodology and load factors for designing bridge piers against ship impact and vehicular collision. Currently, no specific AASHTO design guideline exists for bridges against blast loading. Structural engineering methods to protect infrastructure systems from terrorist attacks are required. This study investigated the most common types of concrete bridges on the interstate highways. A 2-span 2-lane bridge with Type III AASHTO girders was used for modeling. AASHTO Load and Resistance Factor Design methods were used for the model bridge design. The girders, pier caps and columns loading were analyzed for probable blast loading. The model bridge failed under the probable blast loads applied over and underneath the bridge. The research findings show that typical AASHTO girder bridges are unable to resist probable blast loads.
A large number of industrial facilities were damaged during the 1999 Mw7.4 Kocaeli, Turkey earthquake. One of those industrial facilities, Habas plant located within 10 km of the fault trace, provides liquefied gases to commercial plants and medical facilities. Two of the three tanks at the Habas facility collapsed during the earthquake. The main objectives of this paper were to evaluate the seismic performance of tanks and investigate the parameters influencing the dynamic behaviour. Simplified and finite element dynamic analyses of the tanks are carried out including the effect of liquefied gas–structure interaction using a ground motion recorded at a nearby site. The vulnerabilities of the structural system, the observed performance, and damage pattern are discussed by comparing the dynamic analysis results with the strength and deformation capacity of the support columns. The dynamic analysis results from a simplified three-mass model and a finite element model confirmed that the axial and lateral strength of the columns supporting the two nearly full tanks were not sufficient to resist the demand imposed during the earthquake. Consistent with the observed structural performance, an elastic response is predicted for the columns supporting the undamaged 25% full identical tank.
Optimum parameters of a dynamic vibration absorber of non-traditional form have been derived for suppressing vibration of a single degree-of-freedom system due to ground motion. The reduction of transmission of motion from the support to the mass of the structure is compared for the cases of using the traditional and the proposed dynamic absorbers. Under the optimum tuning condition of the absorbers, it is proved analytically that the proposed absorber provides a larger suppression of resonant vibration amplitude of the primary system excited by ground motion than the traditional absorber.
An investigation is undertaken into the bidirectional configuration of the liquid column vibration absorber (LCVA), in which the horizontal and vertical columns may have different cross-sectional areas depending on performance requirements. The bidirectional LCVA appears as a rectangular annulus in plan and mitigates the vibrations of a structure free to move in the horizontal plane by the gravitational restoring force acting on displaced LCVA liquid, energy dissipation occurring through the viscous interaction between the rigid LCVA container and the LCVA liquid, as well as transition effects which occur as the liquid moves between the horizontal and vertical columns of the LCVA. The performance of various configurations of the bidirectional LCVA are studied experimentally when installed on a primary structure subjected to external sinusoidal loading. A theoretical model of the response of the primary structure is presented in which the LCVA is modelled as an equivalent solid mass vibration absorber (SIVIVA) and is found to agree with experimental data. The parameters which allow optimization of the performance of the bidirectional LCVA are investigated, and methods allowing their prediction and control are also presented.
This paper reports the study of the control performance and effectiveness of a new type of passive device—liquid column vibration absorber (LCVA). The LCVA, which allows the column cross-section to be non-uniform, is a variation of the tuned liquid column damper (TLCD). The LCVA provides great versatility and architectural adaptability, since its natural frequency is determined not only by the length of the liquid column, but also the geometric configuration. in this study, an unsteady and non-uniform flow equation for the LCVA is derived based on the Lagrange equation. It is assumed that the liquid flow is uniform in the horizontal and the vertical columns, respectively. The optimal head loss coefficient for the LCVA is derived explicitly under the condition that the LCVA's frequency is tuned to that of the structure. The control effectiveness of the LVCA is numerically analyzed and compared to that of the TLCD and the tuned mass damper (TMD). It is found that if properly designed the LCVA can be as effective as or even more effective than the TLCD.
A hybrid seismic device that provides both energy-absorbing and re-centering capabilities to overcome external forces is developed and evaluated. The hybrid device is composed of three main components: (1) a set of re-centering wires fabricated from shape memory alloy (SMA) material, (2) two energy-absorbing struts, and (3) two high-strength steel tubes to guide the movement of the hybrid device. The SMA wires are located within the guiding high-strength steel tubes and designed to be sufficiently long such that their deformation strain is within the 6% target strain limit. A conservative value of 6% strain, instead of 8%, or 10%, is adopted to (1) avoid the SMA stiffening phase that increases strength up to 5 times that of its forward transformation yield forces, resulting in a serious damage to the adjacent structural members, and (2) to retain the full re-centering capability of the SMA wires even when the hybrid device is under large displacement. The energy-absorbing struts are pin-connected outside of the guiding steel tubes and may be fabricated of mild steel or low strength aluminum. To reduce the possibility of buckling in the energy-absorbing struts when subjected to compression, they are designed to be stocky and seismically compact, or buckling restrained. An optimal proportion of the SMA wires and energy-absorbing struts is formulated such that the hybrid device retains re-centering capability, while maximizing energy dissipation. Results obtained through the seismic analysis reveal that the hybrid braced frame system exhibits a similar energy dissipation capacity to the buckling restrained braced system, while also having excellent re-centering capabilities.
Intensive investigations in the field of the control of structural behaviour have been conducted at the Institute of Earthquake Engineering and Engineering Seismology in Skopje. Part of them, relating to energy absorption elements are presented in this paper. In order to provide a more sophisticated presentation of the characteristics and capabilities of these energy absorption elements, a short review of the currently available and most frequently applied passive control systems is included. To prove the efficiency of the energy absorption elements quasistatic tests on single-span models CR10 and CR20 of the characteristic frame have been performed. The results proved that the CR20 models are of considerably higher strength, even six times higher at ultimate state, ductility and energy dissipation capacity. A mathematical model has been formulated for the nonlinear behaviour of the main elements of the system, whereby a trilinear P-Δ diagram has been used, as developed at the Institute. The analysis of the hypothetical prototype, a five-storey building, with energy absorption elements incorporated in six spans, subjected to the seismic excitations of two PGA levels, 0.12 g and 0.15 g, has shown very good results. Further investigations in this field resulted in the development of new energy absorbing elements (through friction), SBC, which when placed at the joints of the frame introduce hysteretic damping to the structure in the case of low level excitations, when the rest of the system is in the linear range.
Many engineering uncertainties exist in the prediction of integral abutment bridge (IAB) long-term behavior. This paper reports on the development of numerical modeling methodologies formulated on the basis of an extensive field monitoring program and results obtained from four IABs on I-99 in central Pennsylvania. The proposed numerical modeling methodologies allow long-term bridge response prediction, recognizing that an IAB has significant time-dependent response changes as a result of irreversible soil–structure interaction and time-dependent effects of the superstructure in the case of prestressed concrete girders. Both measured and numerical responses indicate that soil–structure interaction and time-dependent effects significantly influence long-term IAB behavior. In addition, relatively low rotational stiffness and nonlinear behavior of common abutment-to-backwall connections influence long-term response. The proposed numerical modeling methodologies are practical and reasonably predict long-term IAB behavior and response under thermal loading.
Remote structural health monitoring systems employing a sensor-based quantitative assessment of in-service demands and structural condition are perceived as the future in long-term bridge management programs. However, the data analysis techniques and, in particular, the technology conceived years ago that are necessary for accurately and efficiently extracting condition assessment measures from highway infrastructure have just recently begun maturation. In this study, a large-scale wireless sensor network is deployed for ambient vibration testing of a single-span integral abutment bridge to derive in-service modal parameters. Dynamic behavior of the structure from ambient and traffic loads was measured with accelerometers for experimental determination of the natural frequencies, damping ratios, and mode shapes of the bridge. Real-time data collection from a 40-channel single network operating with a sampling rate of 128 Hz per sensor was achieved with essentially lossless data transmission. Successful acquisition of high-rate, lossless data on the highway bridge validates the proprietary wireless network protocol within an actual service environment. Operational modal analysis is performed to demonstrate the capabilities of the acquisition hardware with additional correlation of the derived modal parameters to a Finite Element Analysis of a model developed using as-built drawings to check plausibility of the mode shapes. Results from this testing demonstrate that wireless sensor technology has matured to the degree that modal analysis of large civil structures with a distributed network is a currently feasible and a comparable alternative to cable-based measurement approaches.
An analytical investigation is performed aiming at identifying the applicability and the seismic efficiency of an unconventional abutment, which restrains the seismic movements of the bridge deck. The abutment consists of the extension of the deck slab of the bridge onto transversely directed R/C walls with which the, so-called continuity slab, is monolithically connected. The restraining walls play the role of an additional horizontal and relatively flexible support of the deck of the bridge. The design of these restraining walls is based on two criteria referring to on one hand the accommodation of the in-service induced longitudinal movements of the deck and on the other hand on the earthquake loading of the walls. The walls are constructed in a concrete box-shaped substructure, which replaces the conventional wing-walls and retains the backfill material. The foundation of the abutment is checked and found to have adequate resistance against sliding and overturning. The proposed abutment was attempted to be implemented in a precast I-beam bridge. The study showed that the abutment can achieve a desirable control of the seismic movements of the deck and therefore reduces the seismic actions of the bearings, the piers and their foundation. The restraining effect of the abutment is also significant even in stiffer bridge resisting systems.
A comprehensive study carried out to assess the seismic response of a 59-span bridge using a refined inelastic modeling approach and considering Soil–Structure Interaction (SSI) is summarized in this paper. The focus is on describing the methodology adopted to idealize the bridge and its foundation system, while only highlights from the extensive elastic and inelastic analyses are presented. The bridge represents a typical case of vulnerable complex bridges since it was built in the early seventies with minimal seismic design requirements at a distance of about 5 km from a major fault. The SSI analysis is significant in this study due to the length of the bridge, the massive and stiff foundation, and the relatively soft deep soil of the site. A series of three-dimensional dynamic response simulations of the entire bridge are conducted using several analysis tools to verify the developed analytical models. The performance-based assessment study employs 144 site-specific input ground motions representing three seismic scenarios, corresponding to 500, 1000 and 2500 years return periods, to identify areas of vulnerability in the 2164-meter bridge at various hazard levels. It is concluded that the seismic response of the bridge at the 500 years ground motions does not meet today’s standards, while the demands under the effect of the 1000 years ground motions almost exceed the capacity of most bridge components. The demands significantly increase under the effect of the 2500 years earthquake scenario and considerably exceed the collapse limit states. The results clearly reflect the benefit of retrofitting different bridge components to mitigate the anticipated seismic risk. The presented assessment study contributes to improve public safety by exploiting the most recent research outcomes in predicting the seismic response of complex highway bridges, which are essential for developing reliable and cost-effective retrofit strategies.
This study describes numerically, the interdependency between several seismic acceleration parameters and diverse structural damage indices. Peak ground motion, spectral and energy parameters are used for characterising the seismic excitation. On the other hand both, structural and nonstructural damage is considered, expressed by the modified Park/Ang overall structural damage index (OSDI), the maximum interstory drift (ISD) and the maximum floor acceleration. After the numerical evaluation of several seismic parameters, nonlinear dynamic analyses are conducted to furnish the structural damage status. The degree of the interrelationship between the seismic parameters and the damage indices is provided by correlation coefficients. The investigation is carried out for a reinforced concrete plane frame system designed after Eurocodes 2 and 8 (EC2, EC8) and the aim is to determine the characteristics of the accelerograms that exhibit the strongest influence on structural and nonstructural damages. The numerical results have shown, that peak ground motion seismic parameters provide poor or fair correlation with the OSDI, whereas the spectral and energy parameters provide good correlation. Furthermore, the central period and the strong motion duration after Trifunac/Brady exhibit poor correlation with the OSDI. All these results give reason to recommend the spectra and energy related seismic intensity parameters as reliable descriptors of the seismic damage potential.
Dynamic stress and acceleration response analysis of coupled vehicle–bridge systems is important for both bridge safety and vehicle comfort assessment. Nevertheless, a complex finite element model with many degrees of freedom (DOFs) is often required for stress analysis of coupled vehicle and long-span bridge systems, and the mode superposition method may have to be applied to manage the problem. A general procedure for stress and acceleration response analysis of coupled vehicle and long-span bridge systems using the mode superposition method is therefore presented in this paper. The resonance conditions of simple beams under a sequence of equidistant moving loads of identical weights are first analyzed, and the number of vibration modes required in the stress analysis is then discussed. The Tsing Ma Bridge in Hong Kong is selected as a case study to demonstrate the importance of the number of vibration modes involved in the stress analysis based on a comparison with measured stress responses. The acceleration responses of both the railway vehicles and the Tsing Ma Bridge are finally used to evaluate the in-vehicle passenger comfort and track stability. The results demonstrate that the proposed general procedure is feasible and efficient.
Total structural acceleration regulation is a means of managing structural response energy and enhancing the performance of civil structures undergoing large seismic events. A quadratic output regulator that minimizes the total structural acceleration energy is developed and tested on a realistic non-linear, semi-active structural control case study. Suites of large scaled earthquakes are used to quantify statistically the impact of this type of control in terms of changes in the statistical distribution of controlled structural response. Structural responses are shown and statistically characterised for a three-story steel moment-resisting frame with realistic non-linear behavior. Total structural acceleration control is shown to be more effective than typical displacement focused optimal structural control methods, by providing equivalent or better performance in terms of displacement and hysteretic energy reductions, while also significantly reducing peak story accelerations and the associated damage and occupant injury. For earthquake engineers faced with the dilemma of balancing displacement and acceleration demands this control strategy essentially eliminates that concern, making it a very attractive solution to mitigate seismic hazards. These results are also presented in a unique graphical form showing the statistical distribution to highlight the impact of control for a suite of ground motions with a given probability of occurrence. Hence, by presenting structural response in terms of statistical distribution, rather than specific data, the results, as best seen graphically, are immediately applicable to a variety of standard hazard analysis methods, which lie at the core of the trend towards performance-based design in earthquake engineering.
Active vibration control (AVC) via a proof-mass actuator is considered to be a suitable technique for the mitigation of vibrations caused by human motions in floor structures. It has been observed that actuator dynamics strongly influence structure dynamics despite considering collocated actuator/sensor control. The well-known property of the interlacing of poles and zeros of a collocated control system is no longer accomplished. Therefore, velocity-based feedback control, which has been previously used by other researchers, might not be a good solution. This work presents a design process for a control scheme based on acceleration feedback control with a phase-lag compensator, which will generally be different from an integrator circuit. This first-order compensator is applied to the output (acceleration) in such a way that the relative stability and potential damping to be introduced are significantly increased accounting for the interaction between floor and actuator dynamics. Additionally, a high-pass filter designed to avoid stroke saturation is applied to the control signal. The AVC system designed according to this procedure has been assessed in simulation and successfully implemented in an in-service open-plan office floor. The actual vibration reductions achieved have been approximately 60% for walking tests and over 90% for a whole-day vibration monitoring.
An accurate estimate of natural frequencies is essential to correctly predict wind-induced acceleration for serviceability checks in the design of tall buildings. In this study, finite element (FE) models for three tall reinforced concrete buildings were constructed using a popular PC-based finite element analysis program and calibrated to match their fundamental natural frequencies to actual values extracted from the acceleration measurements using the system identification technique. The modification of the FE models for calibration included: (i) consideration of the effect of beam-end-offsets, (ii) modeling of floor slabs instead of using ‘rigid diaphragm assumptions’, (iii) inclusion of major non-structural components such as plain concrete walls and cement brick walls, and (iv) higher elastic modulus of actual concrete than specified value. Natural frequency estimates from the calibrated FE models and the measurements showed remarkable agreement in all the buildings. Using the dynamic properties obtained from the calibrated FE models and the wind-tunnel test results, the acceleration response of one building during a typhoon was predicted and compared with the measured accelerations. Predicted accelerations during the typhoon also indicated a reasonable match with the measured values.
LVDT is generally used as the method for displacement measurement. But this method cannot be applied effectively if the bridge height is so high that it is difficult to install the sensor and the measured results are not as reliable and accurate. In this paper, we suggest the initial velocity estimation method for the displacement determination algorithm to overcome these problems. To verify the proposed algorithm, field tests were carried out. It is also found that the initial velocity estimation method can be effectively applied in the case of bridge displacement monitoring.