Severe Earthquake Action Research Articles

Hybrid Simulation Tests of a Soft Storey Frame Building Upgraded with a Buckling-Restrained Brace (BRB)

Hybrid simulation (HS) is an experimental technique possessing advantages over other testing methods and, in several cases, it is the only available method to test structural systems with reliability. In this paper, HS is used to assess the effects of upgrading a soft-storey frame building using a Buckling-Restrained Brace (BRB). This topic is of paramount significance in seismic regions like Mexico, where more than 40 structures collapsed and thousands resulted with different levels of damage during the September 19, 2017 Mw 7.1 Earthquake. Unfortunately, one of the still-remaining challenges in many seismic countries is the use of seismic protective technologies (SPT) that help to mitigate damages in structures. With the aim of encouraging the use of SPT, this paper presents the results of an experimental program that shows the effectivity of buckling-restrained braces (BRBs) to improve safety and reduce damages in structures with one of the most typical causes of failure, i.e. the soft storey problem. A reinforced concrete five-storey frame building was selected first. Then, a numerical 2D model of the structure was subjected to nonlinear dynamic analyses using several earthquake ground motions. In many analyses, collapse was observed in the structure model. After that, the model was upgraded by introducing a BRB in the soft storey. HS was used to assess the performance of the upgraded structure under severe earthquake action. While the frame building was modelled numerically, the BRB was tested physically. The tests were repeated using a conventional brace instead of the BRB. The results show that introducing the BRB in the soft storey was an effective measure to improve the structure performance under seismic loading; while the disadvantages of the conventional brace were exposed.

Evaluation and prediction of cyclic response of Q690D steel

High-strength structural steel of nominal yield strength greater than 690 MPa is difficult to produce in the hot-rolled condition without heat treatment. Quenching and tempering are thus commonly used to trade ductility for high strength. However, in seismic regions, good ductility of steel structural members is required to endure expected inelastic deformation under severe earthquake actions. This paper describes an experimental investigation on the mechanical properties and hysteretic behaviour of Q690D steel through 29 tensile coupon tests and 14 cyclic loading coupon tests subjected to four different cyclic patterns. The 16 mm and 40 mm quenched and tempered Q690D steel plates used in this study are equivalent to S690Q steel according to EN 10025-6. The test results of Q690D steel were compared with the ductility requirements of current seismic design codes. Under cyclic loading, Q690D steel showed cyclic softening. Based on analysis of the test results, a combined isotropic and kinematic hardening hysteretic model was developed to predict the cyclic behaviour of Q690D steel, with consideration of the Bauschinger effect and cyclic softening behaviour.

09.08: Structural behaviour of steel seismic links under strong cyclic loading

ABSTRACTThe work presented in this paper is part of an extensive European research project on horizontal seismic links subjected to strong full‐reversing cyclic loading. Both experimental testing and numerical simulations were conducted. The link specimens were subjected to combined shear and bending, representing the actual conditions acting on a seismic link during severe earthquake action. Large‐scale tests were performed under constant and increasing amplitude schemes, and parameters studied included steel material grade, length and cross‐section type of the link. The experimental setup employed consisted of a special two‐part steel loading frame that imposed on the steel link specimen a combined bending and shear type deformation. The experiments are supported by finite element model analysis. Three dimensional models have been employed for the simulation of the tests, and the numerical results agree well with the experimental results.

Experimental investigation and modeling of cyclic behavior of high strength steel

With the increase in mechanical strength, the yield to tensile strength ratio becomes more close to 1 and the elongation ratio appears a significant decrease, indicating a deterioration in the ductility and seismic behavior of high strength steel (HSS). For seismic design, understanding of the ductility and cyclic behavior in material level is important to guarantee the abilities of structural steel members to endure expected inelastic deformation under severe earthquake actions. This paper presents an experimental evaluation on the uniaxial cyclic behavior of Q460C steel through 6 cyclic loading tests. The specimens were cut and machined from both steel plates and flanges of hot-rolled H-shaped steel with the nominal yield strength of 460MPa. For the purpose of comparing to normal strength steel, additional cyclic loading test was conducted on Q345B steel. Full hysteretic loops were achieved for HSS as well as normal strength steel. Based on the observations of the test results, a simple piece-wise model was developed for predicting the cyclic behavior of high strength steel, with considering the observed Bauschinger effect and cyclic strain hardening. To verify the accuracy of the proposed hysteretic model for HSS, quasi-static cyclic loading tests of Q460C steel beam-columns were simulated. The comparison between the experimental and predicted moment–curvature curves showed a good agreement, indicating a reasonable efficiency of the proposed trilinear kinematic hardening model in predicting the hysteretic behavior of HSS beam-columns.

The Elastic-Plastic Time History Analysis on High-Rise Steel Structure about Main Power House of Thermal Power Plant

in this paper, elastic-plastic time history analysis was carried out on the new power plant structure jointing the boiler steel frame and high-level framework workshop. Results show that main factory building structure owns rather excellent integration stiffness, good seismic performance and outstanding ability to resist lateral deformation. In addition, the interlayer displacement angle satisfies the requirement of seismic deformation calculation under severe earthquake action.

Dynamic damage criterion and damage mode for single layer lattice shell

When member buckling and joint fractures are considered in the numerical analyses of single layer lattice shells, the relationship curve between peak ground acceleration of the earthquake and the maximum nodal displacement, and the time–history curve of maximum nodal displacement, are erratic and unpredictable. Therefore, with such considerations, the current approach to determine dynamic damage of single layer lattice shells by comparing peak ground acceleration of the earthquake with critical ground acceleration derived from incremental dynamic analysis is inappropriate. An improved structure dynamic damage criterion is proposed for single layer lattice shells in this paper, which reviews the balance status of structure dynamic resistance against the earthquake action, and the structure damage time can be predicted by the occurrence of non-convergent solution to the structural nonlinear dynamic equilibrium equations in the iterative process from the mathematical point of view. Numerical examples are presented to illustrate the simplicity and practicality of the proposed criterion. This criterion serves clear physical meaning and is of considerable potential applicability in analyzing single layer lattice shell structures. Results of parametric analyses of single layer lattice shells under severe earthquake actions indicate that the structure dynamic damage is not determined by material strength failure. For single layer spherical lattice shell, it is determined by structural instability resulted from member buckling; and for single layer cylindrical lattice shell, it is determined by the combined effect of structural instability and the change of structural topology that resulted from member buckling and joint fractures respectively.

Collapse optimization for domes under earthquake using a genetic simulated annealing algorithm

There are two primary collapse scenarios for single-layer latticed shells subjected to severe earthquake action: dynamic instability and strength failure. Of these, dynamic instability is the collapse scenario that must be avoided. First, taking the minimization of the standard deviation of the well-formedness as the optimization objective and the member sections as the optimization variables, an optimization model representing collapse scenarios for single-layer spherical shells is established. This optimization model also accounts for the displacement and stress constraints. Second, a genetic simulated annealing algorithm (GASA) is proposed by combining a genetic algorithm (GA) and a simulated annealing algorithm (SA). Finally, partial and overall optimizations are performed for a single-layer spherical shell that collapses due to instability under earthquake action. The results show that the optimized structure is subject to ideal strength failure under earthquake action with clear warning signs prior to collapse. In addition, the GASA performs better than the GA for optimization. Therefore, it is concluded that the optimization model and method presented in this paper can be used to perform collapse scenario optimization for single-layer spherical shells subjected to earthquake action.

Elastoplastic Analysis and Performance Based Design of a Super High-Rise Building

In order to get the performance of a super high-risebuilding under severe earthquake actions, a fiber-based computational model ofthis structure is established in PERFORM-3D, and both Static Elastoplastic Analysis and Elastoplastic Time-history Analysis are used to evaluate theseismic behavior of this structure. Inter-story drifts at the Performance Point obtained by Static Push-over Analysis are allsmaller than that specified in codes. And results of ElastoplasticTime-historyAnalysis show that structural displacements, shear capacity and flexuralcapacity of some key members all meet the specified performance targets. Thenthis structure is safe.

A Direct Time-Domian Integral Method and its Implementation Based on Matlab

The current equivalent linearization method for evaluation of seismic response of soil layers has been widely used by engineers, but it obviously has limits while considering severe earthquake action and dealing with extremely soft soil layers. Developing a direct time-domain integral method is essential. In this paper, a direct-domain integral method is proposed. In the method, the dynamic skeleton curve constitutive model is introduced and it can fit test results of dynamic shear modules ration curve and damping ratio curve simultaneously, central difference integration method is used to solve the dynamic equation, multi-transmitting artificial boundary condition has been conducted to consider the effect of energy transmission through bedrock boundary. In order to implement this method, a program called Dymatlab has been compiled, strong motion records got from the NGA data base for site effects on strong ground motion have been used to analysis the offshore engineering site with thick soft soil layers. The results show that this program can be applied as a reasonable and feasible method for nonlinear seismic response of soil layers.

Aseismic behaviors of steel moment resisting frames with opening in beam web

Opening in beam web short away clear of beam-to-column connection is an effective method to improve the aseismic behaviors of steel moment resisting frames (MRFs). The pseudo-dynamic (PSD) test and the quasi-static test on the aseismic behaviors of full-size steel MRFs with opening in beam web are carried out. The PSD test shows that the tested frame can satisfy the design requirement and its stiffness isn’t weakened by the web opening. It can be judged from the strain distribution around the beam-to-column connection that the seismic energy is dissipated by local deformation in the weakened area of the beam due to the opening in the case of severe earthquake action, and the expected failure mode of a ductile frame (‘strong column but weak beam’ and ‘strong connection but weak component’) is reached. In the quasi-static test, the failure mode of the tested frame is in conformity with the judgement, i.e., Vierendeel mechanism is formed in weakened areas due to web opening and brittle weld fracture is avoided, which results in an improvement of the aseismic behaviors of steel MRF. Based on numerical analysis, the non-linear analysis model of steel MRF with opening in beam web is provided. Some experimental tests are numerically re-analyzed by applying the proposed model and the numerical results are in conformity with the test results, which verify the validity of the model. A 17-story steel MRF building, damaged during the Northridge earthquake and measured in detail after the earthquake, is selected as the studied case. Push-over analysis shows that the ultimate displacement of the modified building with web openings increases a lot due to the opening and the building’s ductility is improved greatly. Plastic hinge distribution in time-history analysis indicates that brittle weld fracture can be avoided in the frame including connection with opening and the maximum plastic zone moves to the weakened areas. It can be concluded that the aseismic behaviors of steel MRF are improved due to the opening in beam web.

Anti-Seismic Behavior of Innovatory RC Frame Subjected to Severe Earthquake Action

The anti-seismic behavior of RC frame with buckling restrained braces (BRBs) subjected to severe earthquake action in seismic region was investigated in this paper. A design process of the buckling restrained braces used for stiffness-deficiency concrete frame structures was given, the design of the buckling restrained braces was conducted for a common frame structure, the layout of these braces in it was given by taking an actual engineering for illustrations, and the static analysis and time-history dynamic analysis were also performed. The results of computation showed that the use of buckling restrained braces has led to several functional improvements, such as the increase in structure stiffness, reduction of story displacement, and improved energy dissipation ability when compared with the frame without such braces. Analysis results showed further that RC frame with BRBs could absorb and dissipate seismic energy more effectively, improving anti-seismic performance of the framed structure.

Performance of a precast concrete beam-to-beam connection subject to reversed cyclic loading

This study was performed as one phase of an extensive research program focusing on the seismic behaviour of precast connections carried out in Middle East Technical University. The primary objective of the research program was to observe and investigate the seismic behaviour of the connection detail proposed by the collaborating company and the specimens with improved details, in order to develop a “moment resisting precast concrete beam-to-beam connection”. In this study, six beam–beam connection subassemblies were tested under reversed cyclic loading simulating severe earthquake action. The first specimen was a monolithic specimen used as a reference specimen and tested to define the reference behaviour. The second specimen was a precast specimen, which was detailed by a company specializing in precast concrete production. The remaining specimens were modified according to the results of the formerly tested specimens. All of the specimens were identical in dimensions. All test specimens were 1/2.5 scaled models of the improved connection details used in the highly critical earthquake zones. The behaviour of the precast members was compared with that of the reference one and with the others. In order to improve the seismic performance of the connection, several recommendations for future research and practices are also given in the context of the paper.

Damage-reduction-based structural optimum design for seismic RC frames

The development of structural seismic design is briefly reviewed with an emphasis on different conceptual approaches and their success in practical engineering applications. The concept of damage-reduction-based seismic design is proposed, in which the whole structural system is either physically or functionally designed as two parts, the main-function part and the damage-reduction part. The main-function part satisfies the serviceability requirements of the structural system. The damage-reduction part is composed of several damage-reduction elements, which work under hazard loads to ensure the safety of the main-function part, and further maintain the serviceability of the structural system by specific damage-reduction techniques or even by failure of damage-reduction elements. The formulation of damage-reduction-based optimum design for seismic structures is presented and some related issues are addressed, including a simplified approach to reliability analysis, the evaluation of the structural loss expectation, and the modified enumeration method. Numerical examples of RC frames are examined. The results show that several measures of structural seismic performance, including the life-cycle cost, severe earthquake action, and the story-drift reliability index of the weakest story, can be improved by damage-reduction-based design compared with conventional design.