Huanjun Jiang

Discrete element method simulation and experimental validation of particle damper system

Purpose – The particle damper is an efficient vibration control device and is widely used in engineering projects; however, the performance of such a system is very complicated and highly nonlinear. The purpose of this paper is to accurately simulate the particle damper system properly, and help to understand the underlying physical mechanics. Design/methodology/approach – A high-fidelity simulation process is well established to account for all significant interactions among the particles and with the host structure system, including sliding friction, gravitational forces, and oblique impacts, based on the modified discrete element method. In this process, a suitable particle damper system is modeled, reaction forces between particle aggregates and the primary structure are incorporated, a reasonable contact force model and time step are determined, and an efficient contact detection algorithm is adopted. Findings – The numerical results are further validated by both special computational tests and shaki...

Seismic Fragility Assessment of RC Moment-Resisting Frames Designed According to the Current Chinese Seismic Design Code

Abstract Seismic fragility was assessed for 72 RC moment-resisting frame building structures designed according to the current Chinese seismic design code for buildings, taking into account the uncertainty of the structural material strength and earthquake ground motions. The site soil type, the number of stories, and the seismic protection intensity were considered to be the main design variables of the reference structures. Fragilities for four damage levels, i.e., fully operational, operational, repairable, and collapse prevention, are developed in this study. The global seismic damage index, which reflects the effects of individual structural components, and the maximum inter-story drift ratio, which is closely related to the seismic damage of structural and non-structural components, was employed as the damage identifiers. For each frame structure, the probability of exceeding each damage level in an earthquake with a specified PGA was determined by conducting nonlinear time history analysis. Fragility curves for the four damage levels were derived by regression analysis using the nonlinear least-squares method. The structural reliability of RC frames against earthquakes was examined using the developed fragility curves. The results indicate that seismic performance objectives for RC frame structures designed in accordance with the current Chinese code can be achieved with good reliability.

Experimental Study on Damage Behavior of Reinforced Concrete Shear Walls Subjected to Cyclic Loads

Previous experimental research on shear walls has mainly focused on load carrying capacity, deformation, or hysteretic characteristics, with relatively little attention paid to individual damage states and their corresponding responses during the entire loading process until failure. The damage behavior of seven reinforced concrete shear wall specimens subjected to cyclic loading is presented in this study. The effects of the axial load ratio, transverse reinforcement ratio of confining boundary elements, and cross-section shape on damage characteristics, ductility, shear deformation, and crack width of the specimens were analyzed comprehensively.

Damage-control Seismic Design of Moment-resisting RC Frame Buildings

In this study, a new seismic design method for directly and efficiently controlling damage to structural and non-structural components of moment-resisting reinforced concrete (RC) frame buildings is developed. The global seismic damage index, which considers the effect of accumulative damage, and the inter-story drift ratio are applied as the performance indexes for structural and non-structural components, respectively. As the base of this method, the seismic damage model, the determination of the seismic strength demand, and seismic performance objectives are first introduced. Then, the detailed design procedures of this method are presented. Finally, as a case study, the seismic design of a typical 6-story moment-resisting RC frame building structure is provided following this new method. The seismic performance of the designed structure is evaluated under different levels of earthquake by conducting a nonlinear time history analysis. The results indicate that the predetermined seismic performance objectives of the structure as designed in accordance with the proposed method can be achieved with great efficiency.

Damage Displacement Estimation of Flexure-Dominant RC Columns

A semi-empirical method was developed to estimate lateral displacements of flexure-dominant rectangular RC columns at a number of key seismic damage states. The principal damage states studied here include yielding, crushing of concrete cover, significant concrete spalling, buckling of longitudinal bar, and ultimate limit state. At first, the expressions were derived to estimate the compression zone depth of column section by regression analysis on the results obtained from moment-curvature analysis. Secondly, the strain of the extreme compression fiber of the gross section at the onset of concrete cover crushing and that of the confined core section at significant concrete spalling, longitudinal bar buckling, and ultimate limit state individually were derived on the basis of the plane-section hypothesis, plastic-hinge method, and statistical analysis on the database containing the results of cyclic tests on RC columns assembled at the Pacific Earthquake Engineering Research Center. Then the lateral displacement at individual damage state could be obtained by plastic-hinge analysis accordingly. The proposed method can be used as the basis for displacement-based seismic design and damage evaluation for flexure-dominant RC columns.

SHAKING TABLE TESTS ON A COMPLEX HIGH-RISE STRUCTURE WITH TWO TOWERS AND LAPPING TRANSFER COLUMNS

In recent decades, structural engineering tends to progress toward more novel high-rise structures under the requirement of realistic functions and architectural aesthetics. The complex high-rise building structure in this study has two towers with lapping transfer columns. The lapping transfer columns, considering aesthetic requirement in elevation, lead to a complex system of vertical force transfer. The large irregularity in elevation, according to Chinese code, needs a detailed study. A 1/15-scaled model of the structure was tested on the shaking table to evaluate its seismic performance. During the tests, the model was subjected to earthquake inputs representing frequent, basic, rare, and extremely rare earthquakes. The results of shaking table test in terms of the global and local responses as well as the dynamic properties are presented. The tests demonstrate that the designed structural system satisfies the pre-defined performance objectives and the lapping transfer columns are capable of coordinating the bi-level stories to resist lateral forces even under extremely strong earthquakes. To better control seismic damages of the building, some suggestions for improving the design of this structure are also put forward at last.

Seismic Damage Assessment of RC Members by a Modified Park-Ang Model

Quantitative assessment of seismic damage by using damage models has been proved feasible and effective in controlling the earthquake-induced damage of structures. In this study, a modification is proposed for the original Park-Ang model by eliminating its non-normalization problem. The combination coefficient of the modified model is derived using the cyclic test results of flexure-dominant RC members from the database provided by the Pacific Earthquake Engineering Research Center and the authors own tests. An empirical formula is developed through multivariable nonlinear regression analysis to relate the combination coefficient with three design parameters. The comparison between the modified model and the original model indicates that the damage index of flexure-dominant RC members can be determined by the modified model with higher precision and smaller scatter. At last, the damage indexes at principle damage states are calculated by the modified model.

Maximum Displacement Profiles of Reinforced Concrete Frames

Abstract New expressions to estimate maximum seismic lateral displacement profiles of regular plane RC frames at three different damage levels, slight, moderate, and severe damage, are developed in this study for the purpose of displacement-based seismic design. These expressions relating the maximum floor displacements with the maximum inter-story drift ratio over the height and the main structural characteristic of the frame are based on statistical analysis of the results of hundreds of nonlinear time history analysis conducted on a set of 25 plane RC frames subjected to a set of 16 physical accelerograms containing different frequency spectrum. The fundamental period, column-to-beam strength ratio, and damage level were identified as the main structural characteristic having significant effects on the maximum displacement profiles. A case study was conducted on a 12-story RC frame model tested on the shaking table before and shows good agreement between the estimated profiles and test results. The developed profiles are independent of sections and reinforcement of the structure so that they can be used as the starting design variables in displacement-based seismic design.

Performance-Based Seismic Design Principles and Structural Analysis of Shanghai Tower

Shanghai Tower is a 632 m high super tall building adopting innovative steel-concrete hybrid mega frame-core tube-outrigger lateral structural system. Since both of the height and irregularity of Shanghai Tower are far beyond the current Chinese design code provision, non-prescriptive performance-based seismic design (PBSD) approach is required to employ in the seismic design of this super tall building. The general PBSD methodologies of code-exceeding tall buildings are briefly introduced at first. According to PBSD principles of code-exceeding tall buildings, the seismic performance objectives are selected for Shanghai Tower. The design criteria for structural components and systems consistent with the performance objectives are established. The elasto-plastic time-history analysis of the structure under frequent, basic and rare earthquakes, respectively, is carried out with the aid of ABAQUS program. Seven sets of ground motions are selected as the input motions. The detailed numerical simulation results, such as the structural dynamic characteristics, the displacement responses, the base shear, the overturning moment, and the damage conditions, are presented. The structural analysis results indicate that the structure can meet the predetermined performance objectives with relatively large safety margin.

Shaking table scaled model test on a high-rise building with CFT frame and composite core wall

A high-rise building named as Fortune Plaza II Office Building is 264 m high employing the composite system consisting of a concrete-filled steel tube frame and a steel plate reinforced concrete core wall in Beijing, China. The height of the building, the lateral load-resisting structural system and the high seismic intensity level of the construction site present a great challenge to structural engineers. According to the peer review committee’s recommendation, a 1/30 scaled model was tested under a series of one- and two-dimensional seismic excitations with gradually increasing acceleration amplitude. This paper, presents the process of model construction and the results of the shaking table tests. The dynamic characteristics, seismic responses and failure characteristics of the model and the prototype structure are investigated. Based on the test results, the conclusions are drawn that the prototype structure can meet the requirements of performance-based seismic design. The design of the structural system is able to ensure the life safety even when subjected to extremely strong earthquake with peak ground acceleration up to .62 g. Some corresponding measures for improving the design of this structure are also put forward.