Offshore piles are commonly used as foundation elements of various offshore structures, especially large structures such as Tension Leg Platforms (TLP). The stress distribution within such a large structure is a dominant factor in the design procedure of an offshore pile. To provide a more accurate and effective design, a finite element model is employed herein to determine the stresses and displacements in a concrete pile under combined structural and wave loadings. The vertical structural load is essentially a static load, while the lateral wave loading fluctuates in time domain and is directly affected by the incident wave angle. The parametric study will consist of varying certain parameters of the pile to study the effects of the stress distribution under various combinations of structural and wave loadings. Yes Yes
This article discusses the changes in tall building design practice after the World Trade Centre (WTC) buildings collapse. Although many suggestions were made post-9/11, regarding the improvement of the performance of buildings, no major changes have yet been implemented. These suggestions and the lessons learnt from the collapse are discussed in the paper.
In this part, a non-linear 3D finite element model for the analysis of unreinforced masonry walls subjected to static and seismic loads is presented, in order to demonstrate the applicability and potential of the method proposed in Part 1. The work reported here could also stand “on-its-own”, due to the detailed investigation made on this particular subject. The model developed considers masonry as a two-phase material, treating bricks and mortar joints separately, thus allowing for nonlinear deformation characteristics and progressive local failure of both bricks and mortar joints. The influence of the mortar joints is taken into account by using ‘interface’ elements to simulate the timedependent sliding and separation along the interfaces. Analytical and experimental solutions available in the literature have been employed to verify the results obtained from the present finite element model, showing that it is capable of a high degree of accuracy.
The strength reduction finite element method (SRFEM) needs to modify the input shear strength material parameters manually based on various reduction factors, which is trivial. In order to simplify the computation process, the SRFEM can be achieved by using field variables provided by ABAQUS; there-fore, it can be done automatically in software. By deriving the relationship between field variables and reduc-tion factor and getting the corresponding step time t1 when the calculation cannot converge, then it can quan-titatively calculate the stability coefficient of the slope. According to the different decay extent and speed of shear strength parameters c and φ in the process of slope failure, this paper adopted the dual reduction factors finite element method based on field variables for stability analysis of slope, and verified the feasibility of this method in the stability analysis by combining with classic examples, and found that this method not only im-proves computational efficiency but also the calculation accuracy.
Incorporating Graphene Oxide (GO) in concrete composite has been a good alternative to Pristine Graphene due to its hydrophilic nature and its ability to readily disperse in water the consequent cementitious mix. The addition of GO to the cementitious mix has been found to enhance mechanical properties. This paper aims to assess the abrasion resistance of GO incorporated concrete for its application in road pavement design. Experiments for strength in terms of compression, workability in terms of slump and abrasion resistance in accordance with ASTM-C418-20 using a sand-blasting rig are presented in the paper. It is shown that the addition of GO at percentages between 0% to 0.08% (to cement weight ratio), the compressive strength improves by 39% and 26% at 7 days and 28 days, respectively. The addition of GO consequently affected the workability where it was found that the addition of polycarboxylate ether (PCE) (superplasticisers) can drastically improve the workability, which is essential in practical applications. The abrasion was measured for specimens prepared with a high GO percentage between 0.1% to 0.3% and measured at 7 days and displayed a reduction of 70% of abraded volume at 0.3% GO. Finally, the study presents the benefits of using GO where the reduced amount of cement usage will consequently lead to sustainable concrete construction.
Structure's damping force during an earthquake is very different from what was anticipated during design. This adds uncertainty to the process of designing structures exposed to seismic loads which may be a major cause of significant variation in the seismic response reliability of these structures. This work is focused on the investigation of the structural damping uncertainties effect on the structure’s response spectra through the assessment of uncertainties in the damping reduction factors (DRF) derived from the acceleration, velocity and displacement spectra. An Artificial Neural Networks (ANN) was also developed for the stochastic DRF calculation. The Monte Carlo method, one of the methods of computational algorithms that rely on repeated random sampling to obtain numerical results, is used for the estimation of the stochastic DRF. The obtained results indicates that the difference between the deterministic and the stochastic DRF are around of 21 % for displacement and velocity and 28.7 % for acceleration spectra. As a consequence, the DRF derived from the acceleration spectra is more sensible to the uncertainties inherent on damping than the DRF obtained from displacement and velocity. Therefore, it is important to take this conclusion into account when using these factors previously. The ANN constitutes a sample and efficiency method to predict the stochastic DRF since the error obtained is always less than 6 %. Practice oriented results are searched for, to be incorporated in future seismic standards.
In this study a combination of helical springs and fluid dampers are proposed as isolation and energy dissipation devices for bridges subjected to earthquake loads. Vertical helical springs are placed between the superstructure and substructure as bearings and isolation devices to support the bridge and to eliminate or minimize the damage due to earthquake loads. Additionally, horizontal helical springs are placed between the abutments and bridge deck to save the structure from damage. Since helical springs provide stiffness in any direction, a multi-directional seismic isolation system is achieved which includes isolation in the vertical direction. To reduce the response of displacement, nonlinear fluid dampers are introduced as energy dissipation devices. Time history analysis studies conducted show that the proposed bridge system is sufficiently flexible to reduce the response of acceleration. The response of displacement due to provided flexibility is effectively controlled by the addition of energy dissipation devices.
The chemical admixtures named as accelerators improve the early setting and strength of cementations products whereas theh Cement prepared with large volumes of Fly ash (Pozzolana) fetch the durability and better sustainability. Achieving High early strength as well as durability in cementations products is a tough and challenging job which provokes the idea of the addition of accelerators to cement prepared with large volumes of Fly ash (pozzolana). The present study investigated the early setting and strength enhancement of Ordinary Portland Cement (OPC) replacement with 30, 40 and 50% of Fly ash when mixed with the accelerating admixtures such as Calcium nitrate (Ca(NO3)2) and Calcium nitrate (Ca(NO3)2) combination with Triethanolamine (C6H15NO3) at temperature of 25 ± 5 °C and 58±5 % relative humidity. In early ages, the maximum compressive strength was noted for 30 % Fly ash with 1% of Ca(NO3)2 in combinations with 0.05 % of C6H15NO3 and the achieved percentages noted as 18.23% and 54.29% for 1 and 3 days. The microstructural property (SEM) was also determined for OPC replacement with 30% of Fly ash at 1 and 3 days for 1% of Ca(NO3)2 in combination with 0.05, 0.1, 0.15 and 0.2% of C6H15NO3.
This paper presents an overview of the historical development of Australian loading specifications followed by discussions on the regulatory and policy aspects of the development. These included the historical and rational reasons for the development of each individual standard as well as the state of the current system. It is hoped that practitioners will gain some insights into the background and principles underpinning the system that is currently in place.
This paper presents from first principles methods of evaluating the seismic performance of a building using the method of inertial forces, method of maximum energy and method of maximum displacement. The introduction of these methods forms the main thrust of the paper. Importantly, the building can be deemed safe should this be indicated by any one of the three methods none of which requires the natural period of the building nor structural response factors to be estimated. Whilst these methods are very simple and consume little time to apply, the accuracies of the results are comparable with those from response spectrum methods. It is noted that the fundamental basis of each of these methods is very consistent with the new response spectrum model stipulated by the new Australian standard for seismic actions. A succinct and insightful account of the development of the seismic hazard model for Australia is also provided followed by a commentary on the use of dynamic analysis methods in practice.
Effect of elevated temperature on residual mechanical properties of slag based alkali activated concrete (SAC) was compared with Ordinary Portland cement concrete (OPC) when subjected to temperature up to 900 ° C. SAC was prepared using sodium hydroxide and sodium silicate activators. Residual compres-sive strength, tensile strength, flexural strength, modulus of elasticity and bond strength was studied at differ-ent temperature ranges to evaluate effect of high temperature on both concrete. It was observed that compres-sive strength for OPC decreased from 32 MPa to 19 MPa while in SAC variation was decrease was found to be from 32 MPa to 25 MPa. Similarly in SAC variation in residual split tensile, residual flexural strength, re-sidual Modulus of Elasticity and residual bond test was much less compared to OPC concrete. Physical changes were much noticeable in case of OPC at high temperature compared to SAC. This indicates that SAC performed better at high temperature as compared to that OPC.
Minimizing energy usage and increasing occupant comfort are the two primary objectives of in-telligent and eco-friendly buildings. Energy savings of up to 70%, combined with significant occupant pro-ductivity gains are possible via the application of wireless sensor and actuator networks (WSAN). Despite the increasing interests in WSAN-based wireless intelligent lighting control, no prior survey work exists. In the paper, we aim to provide a holistic survey of various WSAN-based schemes for intelligent lighting control so that researchers interested in the field can gain up to date knowledge and inspiration for future research. Spe-cifically, an overview of various sensor data collection and management techniques relevant to lighting con-trol is provided; taxonomy of various intelligent decision making schemes for lighting control is detailed; moreover, open issues within this field are identified and future research directions are proposed.
In recent years Wireless Sensor Networks (WSNs) have been deployed for Building Monitoring (BM) as they provide a low cost and reconfigurable alternative to centralized cable based sensor systems. Using WSNs gives rise to unique issues in its practical usage. Lifetime of a WSN is one such crucial issue to be addressed during deployment. Clustering is an effective way of extending the lifetime of a WSN. In this article we propose a distributed and energy driven clustering algorithm where the selection of the cluster heads (CHs) are based on relative residual energy level of sensors. Furthermore, the CHs are rotated only when their energy drops below a dynamic threshold computed by the algorithm. As a result, the overheads in the inter sensor communications will be reduced and thereby the proposed algorithm will favor more powerful nodes over the weaker ones to prolong the lifetime of the entire WSN. This will effectively prolong the usability of the monitoring system and thus the underlying safety of the building. The results will show that the proposed algorithm performs better when compared to existing clustering algorithms. Further we present theoretical analysis of the performance of the proposed algorithm in terms of correctness and complexity and explain how to identify the optimal values for key parameters such as transmission range R and re-clustering trigger threshold function value C in order to maximize the network lifetime.
An on-line adaptive input estimation method that estimates the moving force inputs of the bridge structure is presented in this research. By using the inverse method, input forces acting on bridge structural system can be estimated from the measured dynamic responses. The algorithm includes the Kalman filter (KF) and the recursive least squares estimator (RLSE). This work presents an efficient weighting factor r of the RLSE, which is capable of improving the estimation results. The capability of the proposed algorithm is demonstrated through several examples of the bridge structure system with different types of the time-varying moving forces as the unknown inputs.
This study investigates the effect of spans length, reinforcement ratio and continuity of flexural reinforcement on the progressive collapse performance of double span beams over failed columns. The investigations focus on initial flexural resisting mechanism to prevent the progressive collapse. Detailed nonlinear finite element simulation of double span beam-column sub-assemblages subjected to residual gravity loads that initially carried by the failed column is adopted for the investigations. Nonlinear static pushover analysis is conducted in which capacity curves are derived and compared with demanded capacities. The effect of spans length, reinforcement ratio and number of continuous bottom flexural reinforcement on progressive collapse are considered in the investigations. Analysis results show that the strength to resist progressive collapse has decreased by 25.4 % and the ductility increased by 103 % following the increasing in span length from 5 m to 7 m. On the other hand, increasing reinforcement ratio of top flexural reinforcement from 0.447 to 1.089 leads to 26.27 % increasing in strength accompanied with a decrease in ductility equal to 16.42 %. In addition, extending all bottom bars rather than the minimum specified two bars resulted in 12 % increasing in strength and 40.28 % decreasing in ductility.
The metro station structure shows different failure modes when it is located at different burial depths. This re-search work is aimed to determine the influence laws of burial depths on dynamic response and failure modes of the metro station under near and far field earthquakes based on the nonlinear elastic-plastic finite element model of the metro station. The research results show that the horizontal displacements and acceleration dy-namic magnification factors of the metro station decrease and especially the internal forces increase gradually when the burial depth increases. The decreasing amplitude of the horizontal displacements and acceleration dynamic magnification factors of the metro station is reduced and the increasing amplitude of the internal forces slows down when the burial depth increases to a specific extent. Therefore, desirable anti-seismic per-formance could be achieved when a specific range of burial depth is avoided reasonably. At last, indoor shak-ing table test for metro station was done, through which we determined the initial failure position and the failure mode of the metro station under earthquake. And shaking table test results demonstrate the validation of the numerical simulation results.
Waste management is becoming a major issue for communities worldwide. Glass, being nonbiodegradable, is not suitable for addition to landfill, and as such recycling opportunities need to be investigated. Due to the high material consumption of the construction industry, the utilisation of waste glass as a partial replacement for fine aggregate in structural concrete is particularly attractive. This project aimed to determine the level of glass replacement resulting in optimal compressive strength. Three concrete samples were tested at 7 and 28 days, for glass replacement proportions of 15, 20, 25, 30 and 40%. Compressive strength was found to increase up to a level of 30%, at which point the strength developed was 9% and 6% higher than the control after 7 and 28 days respectively. This demonstrates that concrete containing up to 30% fine glass aggregate exhibits higher compressive strength development than traditional concrete.
Recycled aggregate concrete (RAC), as a way to reuse waste concrete, is good for solving environmental and resource problems. In this paper, the frost resistance durability of RAC under an extreme cold environment was studied, RAC specimens with different replacement rates were designed, and then the indexes of the specimens, such as mass loss rate, were calculated and compared. It was found that with the progress of the freeze-thaw cycle, the higher the replacement rate of recycled concrete aggregate (RCA) was, the worse the frost resistance durability was. The mass loss rate of RAC-3 (100% RCA replacement rate) was 5.56%, the strength loss rate was 40.86%, and the relative dynamic elastic modulus was 61.89%, all of which were significantly lower than that of RAC-0. The experimental results verify that the excessively large replacement rate of RCA is not conducive to the frost resistance durability of concrete. The replacement rate of RCA needs to be paid attention to when used in an extremely cold environment.
Sustainable concrete construction is critical to the economic development of infrastructures. The need and demand for infrastructure development is crucial to economic and social well-being of all nations. Of all the constituents in concrete coarse aggregate forms the biggest volume. As the reserve of aggregates is finite, the availability of suitable recycled concrete aggregate from demolition of concrete structures provides an alternate source to meet the increasing demand of new construction. Research on recycled concrete
aggregate (RCA) at NUS was first conducted in the 1980’s. In recent years, further studies cover two main areas. The first is on the technique to improve the quality of recycled coarse concrete aggregate by means of microwave treatment. The other is to develop a modified acid treatment method to fully remove all attached materials from RCA coarse particles. This provides a more reliable basis for determination of the mortar content in RCA thus achieving a more precise relationship between properties of RCA and mortar content. Results on the relationship between 24-hour water absorption, bulk density and Los Angeles abrasion resistance of RCA and mortar content show a higher regression coefficient compared to others in published literature.
The paper deals with the experimental investigations done on free vibration characteristics of typical FRP aircraft instrument panel boards made of E-glass /Poly vinyl ester composite. Seventeen panel boards are made using the hand lay-up technique with different number of layers, fibre orientations, thickness and fibre contents. Their physical and elastic properties are determined experimentally. The support conditions and the loadings are simulated in the same manner, as they are located on the aircraft. The first three natural frequencies are determined experimentally. These results are compared with the same results obtained using a finite element analysis software package. Apart from these seventeen boards a number of analytical models with variations in the fibre orientations, the number of layers etc. are also studied and the results obtained are discussed.