Dissertations / Theses on the topic 'Seismic Detailing'

Reinforced concrete frames constructed before the introduction of modern seismic codes have performed poorly during past earthquakes. Such frames have primarily been designed for gravity load effects, leading to light transverse reinforcement in the columns, unconfined beam-column joints, and generally a lack of seismic details required for ductile post-yield behaviour. It has been demonstrated in literature that light transverse reinforcement in a column may result in shear and axial failure. Furthermore, lack of confinement may cause shear failure at joints. However, interaction of vulnerable components and their contribution to the collapse behaviour of existing reinforced concrete frames is not well understood. This research project was initiated to provide a better understanding of the factors contributing to collapse of the frames with non-seismic detailing. In the experimental phase of this study, four 1:2.25 scale, two-bay-two-story specimens were designed with non-seismic details and tested on a shaking table. The target failure mode was intended to be damage leading to collapse that would enable examination of gravity load redistribution during the test. The tests provide unique benchmark data for both qualitative and quantitative assessment of the factors influencing the behaviour of reinforced concrete frames up to the point of collapse. Based on the results from the shaking table tests, this dissertation will evaluate the influence of axial load on shear and axial behaviour of non-ductile columns and the effects of unconfined joints on overall behaviour of a frame near the point of collapse. The analytical phase of the research included evaluation of existing models for predicting shear and axial failure of non-ductile columns and collapse of frames. The currently available models for shear and axial failure of non-ductile columns are mainly drift-based. The results of the current study suggest that these models should be refined using the column ends rotation demand. While results from comprehensive nonlinear models of the four specimens were compared with the test data, simplified models that can be easily employed in engineering practice for assessing existing frames were also evaluated. A refinement to provision from ASCE-41 on column effective stiffness was also proposed in this dissertation.

In this research, monotonic and cyclic tests on cold-formed steel shear walls sheathed with steel sheets on one side were conducted to (1) verify the published nominal shear strength for 18-mil and 27-mil steel sheets; and (2) investigate the behavior of 6-ft. wide shear walls with multiple steel sheets. In objective 1: this research confirms the discrepancy existed in the published nominal strength of 27-mil sheets discovered by the previous project and verified the published nominal strength of 18 mil sheet for the wind design in AISI S213. The project also finds disagreement on the nominal strength of 18-mil sheets for seismic design, which is 29.0% higher than the published values. The research investigated 6-ft. wide shear wall with four framing and sheathing configurations. Configuration C, which used detailing, could provide the highest shear strength, compared to Configurations A and B. Meanwhile, the shear strength and stiffness of 2-ft. wide and 4-ft. wide wall can be improved by using the seismic detailing.

This research investigated the behavior of nonseismically detailed reinforced concrete exterior beam-column joints subjected to bidirectional lateral cyclic loading using nonlinear finite element analysis (NLFEA). Beam-column joints constitute a critical component in the load path of reinforced concrete buildings due to their fundamental role in integrating the overall structural system. Earthquake reconnaissance reports reveal that failure of joints has contributed to partial or complete collapse of reinforced concrete buildings designed without consideration for large lateral loads, resulting in significant economic impact and loss of life. Such infrastructure exists throughout seismically active regions worldwide, and the large-scale risk associated with such deficiencies is not fully known. Computational strategies provide a useful complement to the existing experimental literature on joint behavior and are needed to more fully characterize the failure processes in seismically deficient beam-column joints subjected to realistic failure conditions. Prior to this study, vulnerable reinforced concrete corner beam-column joints including the slab had not been analyzed using nonlinear finite element analysis and compared with experimental results. The first part of this research focused on identification and validation of a constitutive modeling strategy capable of simulating the behaviors known to dominate failure of beam-column joints under cyclic lateral load using NLFEA. This prototype model was formulated by combining a rotating smeared crack concrete constitutive model with a reinforcing bar plasticity model and nonlinear bond-slip formulation. This model was systematically validated against experimental data, and parametric studies were conducted to determine the sensitivity of the response to various material properties. The prototype model was then used to simulate the cyclic response of four seismically deficient beam-column joints which had been previously evaluated experimentally. The simulated joints included: a one-way exterior joint, a two-way beam-column exterior corner joint, and a series of two-way beam-column-slab exterior corner joints with varying degrees of seismic vulnerability. The two-way corner joint specimens were evaluated under simultaneous cyclic bidirectional lateral and cyclic column axial loading. For each specimen, the ability of the prototype model to capture the strength, stiffness degradation, energy dissipation, joint shear strength, and progressive failure mechanisms (e.g. cracking) was demonstrated.

Accounting for blast hazards has become one of the major concerns for civil engineers when analysing and designing structures. Recent terrorist attacks and accidental explosions have demonstrated the importance of mitigating blast effects on buildings to ensure safety, preserve life and ensure structural integrity. Innovative materials such as high-strength concrete, steel fibers, and high-strength steel offer a potential solution to increase resistance against extreme dynamic loading and improve the blast resilience of buildings. This thesis presents the results of an experimental and analytical study examining the effect of high-strength concrete, high-strength reinforcement and steel fibers on the blast behaviour of reinforced concrete columns. As part of the study, a total of seventeen reinforced concrete columns with different design combinations of concrete, steel fibers, and steel reinforcement were designed, constructed, and tested under gradually increasing blast loads using the University of Ottawa shock-tube facility. Criteria used to assess the blast performance of the columns and the effect of the test variables included overall blast capacity, mid-span displacements, cracking patterns, secondary fragmentation, and failure modes. The effect of concrete strength was found to only have a moderate effect on the blast performance of the columns. However, the results showed that benefits are associated with the combined use of high-strength concrete with steel fibers and high-strength reinforcement in columns tested under blast loads. In addition to the experimental program, a dynamic inelastic single-degree-of-freedom analysis was performed to predict the displacement response of the test columns. A sensitivity analysis was also conducted to examine the effect of various modelling parameters such as materials models, DIFs, and accumulated damage on the analytical predictions.

It is important to ensure that vulnerable structures (federal and provincial offices, military structures, embassies, etc) are blast resistant to safeguard life and critical infrastructure. In the wake of recent malicious attacks and accidental explosions, it is becoming increasingly important to ensure that columns in structures are properly detailed to provide the ductility and continuity necessary to prevent progressive collapse. Research has shown that steel fibre reinforced concrete (SFRC) can enhance many of the properties of concrete, including improved post-cracking tensile capacity, enhanced shear resistance, and increased ductility. The enhanced properties of SFRC make it an ideal candidate for use in the blast resistant design of structures. There is limited research on the behaviour of SFRC under high strain rates, including impact and blast loading, and some of this data is conflicting, with some researchers showing that the additional ductility normally evident in SFRC is absent or reduced at high strain loading. On the other hand, other data indicates that SFRC can improve toughness and energy-absorption capacity under extreme loading conditions. This thesis presents the results of experimental research involving tests of scaled reinforced concrete columns exposed to shock wave induced impulsive loads using the University of Ottawa Shock Tube. A total of 13 half-scale steel fibre reinforced concrete columns, 8 with normal strength steel fibre reinforced concrete (SFRC) and 5 with an ultra high performance fibre reinforced concrete (UHPFRC), were constructed and tested under simulated blast pressures. The columns were designed according to CSA A23.3 standards for both seismic and non-seismic regions, using various fibre amounts and types. Each column was exposed to similar shock wave loads in order to provide direct comparisons between seismic and non-seismically detailed columns, amount of steel fibres, type of steel fibres, and type of concrete. The dynamic response of the columns tested in the experimental program is predicted by generating dynamic load-deformation resistance functions for SFRC and UHPFRC columns and using single degree of freedom dynamic analysis software, RCBlast. The analytical results are compared to experimental data, and shown to accurately predict the maximum mid-span displacements of the fibre reinforced concrete columns under shock wave loading.

碩士
國立臺灣科技大學
營建工程系
90
In order to ensure the seismic resistance of beam-column joints, the ACI 318-02 Code requests similar amount of column hoops be detailed within joints to confine the joint concrete. Due to the confinement effect of joint hoops, the seismic capacity of joint is believed to be enhanced. This empirical but heavy amount of joint hoops makes construction work extremely difficult. Moreover, the code-specified joint stress is allowed only if the required amount of joint hoop is detailed. This empirical approach is not suitable for the assessment of seismically insufficient joints, since these joints are usually detailed without hoop. Based on the softened strut-and-tie model, this study developed an analytical model to estimate the degradation curve of joint strength. The beneficial effect of joint hoops is attributable to the tie action instead of confinement. These findings were confirmed by the test of six exterior joint specimens. Four specimens were made of high-strength concrete and the other two were cast with normal-strength concrete. The simplified formulas, based on softened strut-and-tie model, for estimation of joint strength should be helpful for engineers in seismic design and assessment of beam-column joints.

碩士
國立臺灣科技大學
營建工程系
91
The empirical but heavy amount of joint hoops, as specified by the ACI 318 building code for the beam-column joints using high strength concrete, makes construction work extremely difficult. Based on the softened strut-and-tie model, this study is aimed at finding the shear strength and the critical amount of hoops of the interior joints. The critical term means the least amount of hoops to remain in elastic range during seismic attacks. With the reduced amount of hoops, the satisfactory seismic behavior of the joints can be attained and the workability for construction is also preserved. Four interior beam-column joints were tested to investigate the seismic resistance of joints and the role of joint hoops. One specimen was detailed without joint hoop, and the other three specimens were cast using the critical amount of hoops but with different details. The objective of the test program is to clarify the role of joint hoop for seismic resistance.

碩士
國立臺灣科技大學
營建工程系
101
Concrete filled steel tubular (CFT) columns have advantages in strength and ductility. Even under fire attacks, the core concrete could maintain its axial load capacity and thus the strict requirement for fire proof may be liberated. Furthermore, recycling of steel tubes is relatively easy. Typical CFT columns are in the form of square tubes or circular pipes as required by architectural restrictions. Unlike the widely-used box-section columns, the use of circular CFT columns has been limited due to the complexity of the connections to such columns. Recently, skylines in modern cities continue to rise because of urban renewal. The columns in the lower stories in a high-rise building have to sustain high axial load and bending moment. CFT columns have advantages over conventional l and RC columns because the steel tube serves as formwork and offers superior confinement to the infilled concrete, thus improving its strength and ductility under high axial load. However, the complex design and detailing for moment connections have to be further improved, simplified, and verified with experiments. This research proposed a beam-flange-through-type beam-column joint connection for CFT columns and tested four beam-column joint specimens to examine the effect of infilled concrete, beam flange stiffeners, and width of beam on the joint shear strength. Construction of the specimens showed that the proposed connection details are practical and easy to be implemented. Cyclic loading test results showed that the infilled concrete significantly increases the joint shear strength. The use of beam-flange stiffeners and increasing the beam width also have significant contribution to joint shear strength. Current shear strength provisions in the SRC code can be conservatively used to estimate the shear strength of the proposed beam-column joint. However, the shear strength contribution from concrete is significant under-estimated. This research proposed a strut-and-tie joint shear strength model for concrete joint shear strength. Comparison with the test results showed that the proposed model can accurately estimate the shear strength contribution from concrete of the proposed beam-column joint. However, the shear strength contribution from concrete is significantly under-estimated. This research proposed a softened-strut joint shear strength model for concrete joint shear strength. Comparison with the test results showed that the proposed model can accurately estimate the shear strength contribution from concrete of the proposed beam-column joint. Based on experimental obervations and analytical studies, modification to the current code provision on joint shear strength contribution from concrete is proposed. Moreover, the upper and lower limits on the width of the beam flange are proposed to address the constructibility issue related to concrete infilling and shear transfer from the beam to the joint. Furhermore, design suggestions on the beam flange stiffeners are proposed.

碩士
國立臺灣科技大學
營建工程系
88
This paper studied the hoop details in the beam-column joints with high-strength concrete. The ACI 318-95 Code assumes the transverse reinforcement to confine the core concrete of the joints. Therefore, the ACI requirements of joint hoops are directly proportioned to fc''. In the cases of high strength concrete, the ACI requirements result in congested joints which are very difficult to construct. Based on the softened strut-and-tie model for strength prediction, the joint hoop is expected to be replaced with the beam web reinforcement under a promise to satisfy the strength requirement. The primary variables in this study were the size and amount of the beam web reinforcement. Totally five corner beam-column joints were tested. Experimental results shows that the shear strength of joint has a pronounced effect on the ductile behavior and ability of energy dissipation. On the other hand, the requirement of hoop reinforcement could be relaxed for the joints with sufficient strength. The yielding of the beam web reinforcements was observed as a result of their participation in beam flexure. The yielding beam bars would have had no spare tension capacity to act as tension ties. It is therefore concluded that beam web reinforcement could not be used as a complete replacement for horizontal core reinforcement.

碩士
國立臺灣科技大學
營建工程系
103
Low-rise reinforced concrete street residential buildings are a common building type in Taiwan. Due to the need for ventilation, lighting, and passageway, the walls of such buildings along the street direction typically have a significant amount of opening, resulting in a significant reduction in the seismic capacity of the walls. As a result, many of such buildings showed severe damage along the street direction in the 1999 Chi-Chi earthquake. Currently, there is no simple and effective means in the engineering community for the seismic evaluation of the walls of such buildings along the street direction. The 2013 ABRI research project, “Seismic behavior of exterior walls with typical opening of low-rise reinforced concrete street houses,” studied the effects of types, sizes and locations of opening on the seismic behavior of exterior walls in the back side of the buildings. Suggestions on seismic design and evaluation of the exterior walls were proposed. The study also indicated that the exterior wall of the first story typically contains a higher area of opening than those of the other stories. This caused soft-story failure mechanism typically seen in the 1999 Chi-Chi earthquake. To upgrade the seismic capacity of exterior walls in the first story of low-rise reinforced concrete street residential buildings, three methods are proposed in this research: (1) boundary elements at the two sides of openings; (2) confinement reinforcement; and (3) diagonal reinforcement. Construction of full-scale walls showed that the proposed upgrading methods are feasible. Moreover, casting of the upgraded walls showed little voids and segregation of concrete. Cyclic tests of upgraded walls showed that the use of boundary elements increased the strength, ultimate drift, and energy dissipation by 21%, 20% and 50%, respectively. The use of confinement reinforcement and boundary elements induced unexpected shear friction failure. Further research on this issue is needed. The use of diagonal reinforcement, confinement reinforcement and boundary elements increased the strength, ultimate drift, and energy dissipation by 50%, 150% and 317%, respectively.

碩士
臺灣大學
土木工程學研究所
98
Codes of practice of Europe and United States of America are shared with many countries in the world. In fields of civil and structural engineering, EN Eurocodes and ACI codes (American Concrete Institute) are commonly used and they have been constantly updated according to technology advancement of human beings. Many countries have adopted EN Eurocodes or ACI codes as their national codes. The author would like to focus this study on the common construction problems in high rise buildings encountered in Vietnam, which deals with wide beam-column joints, beam-core wall joints, coupling beams and deep beams. These construction problems are first briefly described. The related seismic design and detailing are then compared and evaluated by using the EN 1998-1:2004 and ACI 318-08 codes. This study is expected to clarify some common mistakes and to improve the construction practice in Vietnam.

碩士
國立臺灣大學
土木工程學研究所
99
Reinforced concrete buildings in seismic zones has been limited to low-rise or medium-rise buildings worldwide, because of a lack of structural safety against earthquake. A high-rise reinforced concrete building can be built with the aids of the structural walls which provide lateral resistance efficiently. Architectural considerations usually result in window and door openings in structural walls, which divided a single wall into more slender walls connected by short or deep beams, referred to as coupling beams. This research forcuses on the seismic behavior of coupling beams. The exrimental program is divided into two parts. The fisrt part is to test specimens with l_n⁄h=3 and the other is to deal with l_n⁄h=1. The parameters invove mainly with the different detailing of coupling beams. All specimens are subjected to double curvature bending moment were tested quasi-syatic loading. Test results shows that the performence of specimens using vertically distributed reinforcement are not improved, but the specimens with increased confinement can enhance their post-strength behavior. This research also proposed an analytical model to predict the shear strength of coupling beam.