Shyh-Jiann Hwang

National Taiwan University | NTU · Department of Civil Engineering

Engineers design structures based on physics, experiments, andexperience. But due to increasing demands, structures today are being built at scales that far exceed experience and experimental testing. Bažant summarized the problem well in 1984: “Most laboratory tests are carried out on a reduced scale, from which generalizations must be made for mu...

Reinforced concrete flat plate systems are widely adopted in buildings owing to ease of construction and facilitating larger clear story heights. Flat plates are routinely designed for two-way shear to preclude brittle punching failures. Accurate assessment of concrete contribution to shear strength is particularly important for flat plates in carr...

Nonlinear static pushover analysis has been widely used for the seismic assessment of building structures. It can predict not only the base shear and deformation capacity of buildings but also the acceleration response of each floor. The floor acceleration is a significant design parameter for nonstructural components. The National Center for Resea...

Reinforced concrete structural walls are major vertical lateral load‐resisting members in reinforced concrete structures located in seismic regions. It is important to understand and evaluate the hysteresis behavior of these members for an efficient earthquake‐resistant design. Among the various models available for estimating this hysteretic behav...

There are too many reinforced concrete (RC) columns built before mid-1970s without sufficient transverse reinforcement. By now, we understand quite well the importance of transverse reinforcement in allowing a column to maintain its integrity under large displacement reversals in the nonlinear range of response. Poorly confined RC columns undergo a...

This paper presents the image-based measurement for a set of reinforced concrete (RC) wall experiments. The experiments were carried out at the multi-axial testing system (MATS) in National Center for Research on Earthquake Engineering (NCREE) in Taipei, Taiwan. Four specimens of RC walls with different aspect ratios, tie spacing, axial forces were...

The use of high-strength concrete (HSC) in high-rise buildings can reduce the size of structural members and increase the residential space. However, the behavior of HSC at ultimate loads is more brittle than that of normal-strength concrete. Hence, the ACI 318-19 building code requires that all the column longitudinal bars be confined by seismic h...

Reinforced concrete (RC) walls containing openings are usually stiffened by boundary elements (or boundary flanges) in the form of columns on one or both sides. Both thickness and longitudinal reinforcement ratio of such boundary members generally exceed those of enclosed walls. Such boundary elements also contribute to an improvement in the streng...

Flat slabs are characterized by an absence of beams framing into columns. The limited depths of flat slabs result in the development of severe stresses near the column-slab joints, which typically results in brittle punching of the column into the slab, especially when transverse reinforcement is not provided. It is thus important to accurately ass...

Reinforced concrete structures exhibit a sudden and catastrophic drop in load-bearing ability when shear failure is encountered. Therefore, practicing engineers often provide great importance to preclude such brittle failures in any part of the structure. It is generally addressed by either increasing the member depth or using tension reinforcement...

The post‐earthquake system identification and response estimation of an elastic 13‐story compound building during four seismic events were effectively conducted using a simplified numerical model: the generalized building model (GBM). The compound building examined was the recently remolded office building of Taiwan's National Center for Research o...

Reliable hysteretic modeling is essential for the evaluation of existing reinforced concrete (RC) buildings. Also, tall buildings and other structures of high importance require reasonably accurate seismic nonlinear time‐domain analysis for design, which includes load–displacement behavior and hysteretic modeling. However, the hysteretic behavior o...

A 7-story reinforced concrete building with a soft bottom story and plan-asymmetry in one horizontal direction was collapsed on a shake table by generation of bi-directional near-fault ground motions. The numerical model of the 7-story building is introduced and verified through a comparison with the experimental results. The hysteretic models of t...

Many residential buildings in Taiwan use reinforced concrete (RC) walls with openings; the stiffness and strength of the walls with openings greatly influence the structural seismic behaviors. Neglecting the lateral capacities of these RC walls with openings may cause mispredictions of seismic evaluation and may lose the economy of seismic retrofit...

Reinforced concrete pile caps are important structural elements transmitting vertical loads from the structure to the ground. The performance of pile caps is complex, with a wide range of structural parameters in play, such as geometry, tension reinforcement, pile arrangement, and so on. Their complexity and criticality demand a good degree of reli...

The shake table tests presented in this article aims to explore seismic displacement demands for existing reinforced concrete buildings resulting from inelastic torsion associated with different sources of irregularities. Two half-scale seven-story reinforced concrete structures were subjected to unidirectional earthquake excitations on the shake t...

The near-fault effect on buildings and infrastructures is a significant issue of human life and property in Taiwan because there are numerous active faults inside this island. It is well-known that special characteristics with large displacement and high velocity can be observed close to a near-fault. However, it is difficult to reproduce such a ne...

Soft or weak stories are defined as stories in buildings that are more flexible or weaker than adjacent stories. These stories can be vulnerable to damage and collapse during strong earthquake ground shaking, especially when the story is supported by reinforced concrete columns susceptible to shear failure. To effectively evaluate and retrofit such...

Reinforced concrete pile caps are commonly used in the foundations of buildings and bridge structures. The design of pile caps should be carried out judiciously, considering both the bearing capacity of the soil and the strength of the pile caps. Pile caps experience significantly high punching shear forces transferring the load from the structure...

Reinforced concrete pile caps that connect columns and piles are a part of foundation systems. Pile caps transmit high axial loads from the structure to the ground. In tall buildings, the pile caps experience severe punching stresses, often resulting in brittle failure. These foundation elements are very crucial as any damage to pile caps can risk...

An earthquake with an epicenter offshore of Hualien City in eastern Taiwan occurred at midnight on February 6, 2018. The Richter magnitude (ML) of the earthquake was 6.26 and the seismic intensity ranged up to level VII, the strongest seismic intensity level regulated in Taiwan. Almost all the major damage resulting from this seismic event was occu...

The shear capacity of reinforced concrete knee joints in closing and opening actions are determined in this paper using the framework of the softened strut-and-tie model. The proposed model considers the closing and opening actions separately and takes into account the differences in joint behavior to accurately predict the joint capacity in closin...

According to the previous earthquake reconnaissance, existing reinforced concrete buildings with intermediate short columns are vulnerable to shear failure. Thus a simulation of the behavior of intermediate short columns has a significant influence on the seismic evaluation. This paper tests eight intermediate short column in shear failure cases wi...

A high performance seismic simulation shaking table, which is located in Tainan Laboratory of the National Center for Research on Earthquake Engineering (NCREE), was established to reproduce the near-fault ground motion. The maximum horizontal stroke and velocity capacities of the shaking table are ±1.0 m, ±2.0 m/sec, respectively. The 2016 Meinong...

Cities in seismic regions often have unknown numbers of older buildings vulnerable to strong earthquake ground motion. Simple methods are needed with urgency to screen these buildings. The problem is of immense proportions as it affects some of the largest cities in the world. Seismic vulnerability indices proposed by Hassan and Sozen (ACI Struct J...

Based on recent reconnaissance observations, the plastic hinge zone or D-region of structural members is vulnerable under earthquake loading. These types structural members are usually dominated by shear behavior due to inadequate reinforcement. Based on the macro models for D-regions, there are two different types of concrete strut: the bottle sha...

An analytical method is proposed to predict the shear strength of reinforced concrete deep beams with web openings and to evaluate the associated failure mode and its corresponding position. The proposed method aims to define the shear-transfer paths in reinforced concrete deep beams with web openings based on the strut-and-tie concept, and to dist...

The reinforced concrete squat wall, which demonstrates high stiffness and load capacity, is one of the most effective earthquake-resisting members. It has been widely used in seismic design and retrofitting and thus is crucial to an understanding of the lateral load-displacement behavior within. Based on the strut-and-tie concept, a trilinear model...

A geometric discontinuity caused by abrupt changes in cross-sec-tional dimensions and a force discontinuity caused by concen-trated loads results in discontinuity regions due to the disturbance in the flow of internal forces. A softened strut-and-tie model has been developed for determining the shear strength of discontinuity regions that fail unde...

C urrent ACI 318 code requirements for determining the shear strength of concrete beams are separated into two distinctly different methods: one for nonprestressed reinforced concrete (RC) and one for prestressed concrete (PC). 1 This design methodology is very confusing and difficult for engineers to understand, as multiple equations are used to d...

Reinforced Concrete (RC) buildings are often subjected to multi-directional loadings under earthquake ground motions due to the structural configuration and inherent multi-dimensional earthquake motions. Previous researches have been focused on individual components with a few bi-directional tests. Essentially no research data, including experiment...

Short columns in buildings are generally the members with high stiffness and governed by brittle shear failure. Therefore, lateral load displacement curves for short columns have significant influence on the seismic assessment. In this study, a trilinear relationship is proposed to simulate the seismic behavior of short columns failed in shear with...

The seismic performance of intermediate clear span-depth ratio (2.0 ≤ ℓn/h ≤ 4.0) coupling beams with hybrid layout were evaluated in this study. By combining the conventional ductile beam detailing and the benefit of the presence of diagonal bars, this study shows that the hybrid layout may serve as one of the possible alternatives to ease constru...

The usable land is quite limited in Taiwan now, so that the construction of ultra high-rise residential building using high strength reinforced concrete materials is inevitable. In practice, short columns are often resulted due to openings and their shear strength prediction is very important. Observation from experiments shows that shear failure o...

The proposed method, called the Taiwan Earthquake Assessment for Structures by Pushover Analysis (TEASPA), is a modified capacity spectrum method developed in the NCREE handbook after the 1999 Chi-Chi earthquake. In this study, the evaluation of TEASPA is carried out using results from an experimental campaign comprised of two pushover tests inlow-...

A reduced-scale, planar, two-story by two-bay reinforced concrete frame with weak beam-column joints was subjected to earthquake simulations on a shaking table. The beam-column joints did not contain transverse reinforcement, as is typical in older construction designed without attention to detail for ductile response. A series of linear and nonlin...

This paper reports the results of cyclic loading tests performed on four specimens consisting of reinforced concrete frames with brick infill walls. The brick infill is pre‐laid, followed by the cast in‐place RC columns and beams. Test parameters include the height‐to‐length ratio of the brick infill wall and the mortar compressive strength. Test r...

Damage to buildings observed in recent earthquakes suggests that many old reinforced concrete structures may be vulnerable to the effects of severe earthquakes. One suitable seismic retrofit solution is the installation of steel braces to increase the strength and ductility of a building. Steel bracings have some compelling advantages such as their...

The ACI 318-14 design procedure for a diagonally reinforced coupling beam is questioned because it proportions the amount of diagonal reinforcement to meet shear demands by completely neglecting the participation of concrete and failing to recognize any flexural strength that may be developed. This ACI 318-14 design procedure might introduce unnece...

Damage to buildings observed in recent earthquakes suggests that many old reinforced concrete structures may be vulnerable to severe earthquakes. One suitable seismic retrofit solution is the installation of steel braces to increase the strength and ductility of a building. In this study, the braces were connected to gussets furnished with anchor b...

Using high-strength reinforcement and concrete have many advantages, including smaller member sizes, lighter structure elements, lesser reinforcement, longer span capability, and more space available for end users. Also, high-strength concrete structures are usually sustainable. This project investigate how to extending current design methods for f...

Reinforced concrete (RC) frame with brick infill is a common structure system of existing low-rise RC building. Therefore, it is essential to study the seismic behavior of RC frame with brick infill. An evaluating procedure for the seismic performance of RC frame with brick infill can be found in ASCE/SEI-41. In accordance with ASCE/SEI-41, the tra...

Short columns are designed as structural members having a high stiffness with low ductility and governed by brittle shear failures. During an earthquake, short columns are often the first members to fail. Therefore, their stiffness, strength, and collapse behavior are significant to the seismic evaluation of building structures. This study conducte...

A new equation for the shear strength of non-prestressed reinforced concrete (RC) beams is proposed. The proposed equation is consistent with the shear strength equation for prestressed concrete (PC) beams proposed by Laskar et al. Both equations have the same variables for shear span-depth ratio (a/d)-0.7, the strength of concrete f'c , and the we...

This paper presents a new treatment to predict the shear strength and failure mechanisms which include concrete crushing and steel yielding for reinforced concrete deep beams with web openings. The proposed method is derived from the concept of struts and ties, and it also satisfies the equilibrium, compatibility, and constitutive laws of cracked r...

Four reinforced concrete frame specimens were tested on a shaking table with the objective to observe the interaction of structural elements at the onset of collapse. Each specimen consisted of a 1/2.25 scaled model of a two-bay, two-story reinforced concrete frame without seismic detailing. The specimens were tested under moderate and high column...

All types of school buildings were seriously damaged in Taiwans 921 Chi-Chi earthquake. Seismic evaluation and retrofit of these numerous vulnerable school buildings has become an important issue to be resolved. The National Center for Research on Earthquake Engineering (NCREE), Taiwan assisted the Ministry of Education on the arrangement of progra...

Based on test results made of normal-strength reinforced concrete, Joint ACI-ASCE Committee 352 has developed design recommendations for joints of special moment frames including requirements of moment strength ratio, shear strength, confinement, and development length. Due to the interests of the reinforced concrete industry in using high-strength...

: This paper describes an experimental and analytical study in reinforced concrete frames with weak beam-column joints. A 1/2.25 scale, planar, two-story by two-bay reinforced concrete frame was subjected to earthquake simulations on the shaking table. The beam-column connection did not contain transverse reinforcement that is typical in older-type...

Detailed observations are reported for eight shear wall buildings from the Concepcion region that experienced severe damage during the 27 February 2010 Chile earthquake. The repetitive nature of some of the damage suggests that these field observations may be applicable to similar buildings elsewhere, whereas other damage may be unique. Several she...

Seismic retrofitting of existing school buildings is a significant issue in Taiwan. Compulsory school buildings often have many openings along their corridors. Here, rather than attempting to change existing doors and windows, it seems convenient to retrofit the confined brick walls between classrooms with carbon fiber reinforced plastic (CFRP) to...

Column plays an important role as a vertical and lateral load carrying member in building structures. In order to reduce the dimension of the lower-story columns of high rise buildings, the use of high strength materials has become an effective measure. However, most of the available experimental data on the high strength columns came from the test...

This paper presents the development of an analytical model that accounts for the force transfer mechanism and shear strength of reinforced concrete (RC) beams. The transfer mechanism of shear forces in RC beams can be characterized based on their load paths in the disturbed and the beam regions. This study proposes that the domains of these differe...

A simplified method, developed from the softened strut-and-tie model, for determining the mid-span deflection of deep beams at ultimate state is proposed. The mid-span deflection and shear strength predictions of the proposed model are compared with the experimental data collected from 70 simply supported reinforced concrete deep beams, loaded with...

In order to observe the interaction of structural elements at the onset of collapse, four frame specimens were tested at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan in spring 2009. Each specimen consisted of a 1/2.25 scaled model of a two-bay and two-story reinforced concrete frame. The specimens were tested under m...

ASCE/SEI 41, the standard for seismic rehabilitation of existing buildings, proposes seismic evaluation procedures for concrete buildings. In-situ test results of existing school buildings in Taiwan can be used to verify the evaluation methodology in ASCE/SEI-41 Supplement 1. This paper reports on one in-situ specimens, 2-story 2-classroom building...

Post-earthquake reconnaissance has reported the vulnerability of older reinforced concrete (RC) columns lacking details for ductile response. Research was undertaken to investigate the full-range structural hysteretic behavior of older RC columns. A two-dimensional specimen frame, composed of nonductile and ductile columns to allow for load redistr...

In this study, 15 reinforced concrete corbels with shear span-to-depth ratio greater than unity were tested. Test results indicate that the shear strength of corbels increases with increase in compressive strength of concrete, parameter of main reinforcement and parameter of vertical stirrups. The shear strength of corbels also increases with decre...

Tests on a 2-story RC building subjected to bi-directional reversed cyclic loading have been performed to examine the torsional effect caused by the eccentricity at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan. This is an internationally-cooperated project between NCREE and the University of Houston (UH). In order to...

Several studies showed that the eccentricity between beam and column connections has a detrimental effect on the joint shear strength. With regard to this issue, ACI 318-08 restricts the average shear stress on a horizontal plane within the joint, which equals to the effective joint width times column depth. The formula of effective joint width giv...

Many low-rise school buildings in Taiwan suffered severe damages during the Chi-Chi Earthquake, and these buildings revealed the poor capacity of earthquake resistance. How to estimate the seismic capacity of existing school building is an important issue. Therefore, an in-situ pushover test of the existing school buildings in the Sin-Chen Junior H...

RC short columns are prone to pure shear failure due to insufficient transverse reinforcement, but there has been very limited research found in the literature on pure shear failure of short columns. As such, this study conducted shaking table tests on 4 specimen frames to investigate full-range structural behavior of RC short columns until complet...

This study presents a model to better understand the shear behavior of reinforced concrete walls subjected to lateral load. The scope of the study is limited to squat walls with height to length ratios not exceeding two, deformed in a double-curvature shape. This study is based on limited knowledge of the shear behavior of low-rise shear walls subj...

Guidelines have been developed in the United States to assist in the design of buildings resistant to progressive collapse. These guidelines outline several methods for incorporating the dynamic amplification on load redistribution that occurs when there is sudden member failure in a structure. Analytical studies have been performed to evaluate the...

Collapse experiments are found very helpful in facilitating collapse analysis of new buildings and identification of older buildings that are at high risk of structural collapse during severe earthquake events. Experimental observations from dynamic global collapse of a single story 3-bay RC frame are presented in this paper. The frame is composed...

An analytical study of load-deflection responses of double-curvature reinforced concrete squat walls is summarized in this paper. Prediction of load-deflection responses consists of cracking, ultimate, and post strength points. The cracking point in the load-deflection curve is calculated using a procedure of strength-of-materials. The ultimate str...

This study elucidates the prediction of ultimate strength and corresponding deflection of low rise shear walls subjected to lateral load. The scope of the study is limited to low-rise shear walls with height to length ratios not exceeding two, and walls due to lateral load are deformed in a shape of double-curvature. This study is based on limite...

On May 27, 2006, an earthquake of 6.3 in magnitude struck Yogyakarta and Central Java areas. National Taiwan University of Science and Technology, National Center for Earthquake Engineering, and National Science and Technology Center for Disaster Reduction composed a reconnaissance team of 16 members to carry out a five-day field investigation in t...

At 1:47 a.m., September 21, 1999, an earthquake of magnitude 7.3 rocked central Taiwan and resulted in more than 2,600 deaths and 8,000 injuries. Violent ground shaking and significant surface faulting destroyed or damaged more than 8.700 buildings. The experiences from Chichi earthquake can provide useful information to the design and construction...

This paper mainly presents the observation results of structural damages in the affected region of 2006 Yogyakarta earthquake. The observed buildings consist of public buildings, residential buildings, and historical buildings. In case of the public buildings, the observation shows that most of low rise RC buildings were damaged due to a common fai...

Performance-based design methodologies require a thorough understanding of the lateral and vertical load behavior of the structural elements for all levels of performance, including collapse prevention. It is, therefore, important to assess the accuracy of analytical models used to predict the collapse behavior of structural elements. The current p...

This paper studies the force transferring mechanisms and shear strength of reinforced concrete (RC) beams. The transferring mechanism of shear forces in RC beams can be characterized as the load paths in the disturbed regions and the beam regions. The domains of different regions are proposed to be determined by the beam geometry, the longitudinal...

The 1999 Chi-Chi earthquake revealed the poor performance of the RC school buildings in Taiwan. It also indicates an urgent need of seismic evaluation and retrofit for the remaining schools. In order to realize the behavior of a typical school building subjected to lateral load, a series of in-situ test for two existing 2-story RC school buildings...

Recently structural collapse has gained broader attention worldwide in view that collapse analysis is the critical component in fully realizing performance-based design concept especially for the near- fault and 2/50 hazard levels. Since 2004, NCREE has conducted a series of global collapse experiments on its 5m×5m earthquake simulator. This paper...

This paper summarizes a study of the force displacement response of reinforced concrete walls resisting shear forces in the plane of the wall. The scope of the study is limited to squat walls with height to length ratios of approximately two and less. For reinforced concrete walls subjected to lateral loading, the sources of flexibility leading to...

This paper evaluates the softened truss model and the softened strut-and-tie model for predicting shear strength of reinforced concrete squat walls. The prediction accuracy of analytical solutions is examined using the experimental data of 62 test shear walls available in the literature. It was found that the analytical solutions, which utilize the...

This study investigated the effect of joint hoops on the shear strength of exterior reinforced concrete beam-column joints subjected to earthquake-type loading. Nine exterior reinforced concrete beam-column subassemblages were tested under reverse cyclic loading. All test specimens were designed to have adequate shear strength of joints, determined...

For seismically insufficient buildings, retrofitting of the reinforced concrete partition walls using the carbon fiber reinforced polymer is of particular interest at the present juncture in Taiwan after Chi-Chi Earthquake. This paper describes theoretical and experimental studies related to the seismic retrofits of the reinforced concrete frames c...

In this study, 24 high-strength concrete dapped-end beams were tested to study the effects of the amount of main dapped-end reinforcement, the nominal shear span-to-depth ratio, and the concrete strength on the shear strength of dapped-end beams. Test results indicate that the shear strength of dapped ends increases with the increase in the amount...