Vol.36/No.2 (140) (2021)


TitleLong-Span Buckling-Restrained Braces using Truss-Confined Restrainers
AuthorChun Chen, Yu-Cheng Lin, An-Chien Wu, Lu-An Chen, Keh-Chyuan Tsai
Keywordsbuckling-restrained brace, mega brace, truss-confined restrainer, flexural rigidity, shear rigidity, stability analysis
AbstractLong span buckling-restrained braces (BRBs) are getting popular for applications in seismic tall buildings. Recently, a novel type of BRB, namely the truss-confined BRB (TC-BRB) with a constant-depth truss built into the restrainerhas been investigated. The TC-BRB’s restrainer is constructed by attaching an additional truss system composed of several steel open-web truss frames outside the central steel casing in order to develop the overall restraining rigidity. Thus, the cross-sectionof the central steel casing and the weight of the infilled mortar in the TC-BRB can be significantly reduced in comparison with the conventional BRBs. The initial crookedness caused by the BRBs’ self-weight can also be reduced in the cases of long-span and large axial capacity BRB designs. This study investigates a new type of TC-BRB using a varying-depth truss system in the restrainers. This type of TC-BRB could save construction material and achieve the structural aesthetic more effectively than those using the constant-depth trusses. In this study, stability analytical model and seismic design procedures are developed and verified. Key mechanical properties including equivalent flexural rigidity and shear rigidity of the truss system are firstly presented. It is illustrated that the TC-BRBs’ elastic flexural buckling strength (Pcr) can be satisfactorily computed by incorporating Timoshenko shear effect into the classical stability theory. TC-BRBs’s buckling failure strength (Plim) can be further computed by considering the initial imperfections and inelastic material property.Abaqus finite element model (FEM) analysis results indicate that the proposed analytical model can satisfactorily predict the restrainers’ Pcr with errors less than 10%; and predict the TC-BRBs’ Pcr with errors less than 3%. In the first phase experiment, two 1/5-scale TC-BRB specimens, each of 6.3m long with the 1016-kN nominal yield strength anda constant- or varying-depth truss design, were tested in NCREE. Cyclic test results confirm that the Plim of the two TC-BRB specimens can be accurately predicted using the proposed analytical model with errors less than 6% when the effects of residual stresses in the truss members are considered. In the second phase experiment, two additional specimens were fabricated with significantly increased stability capacities. Cyclic test results show that the Plim of these two specimens can also be accurately predicted with the errors less than 7%, further confirm the reliability of the proposed analytical model. The TC-BRBs’ experimental performance also suggests that the proposed design procedures are generally conservative and practical. This study concludes with the recommendations, produres and examples on the seismic design of the proposed TC-BRBs using the constant- or varying-depth trussses.
TitleThe seismic performance of reinforced concrete columns using the lap-spliced crosstie with various axial load
AuthorTai-Kuang Lee, Cheng-Cheng Chen
Keywordslap-spliced crosstie, lap splice length, axial tension, RC columns, seismic performance
AbstractA lap-spliced crosstie consists of two J-shaped steel bars (rebars) that have a straight end and an end featuring a 180° hook. In this study, the cyclic lateral load test of four large-scale reinforced concrete columns with axial force proportional to the lateral force was conducted to discuss the seismic performance of RC columns with lap-spliced crossties and investigate the axial tension load effect. The research results are presented as follows: (a) The seismic performance of the specimens that adopted lap-spliced crossties is superior to that of the specimen using conventional crossties and worse than that of the specimen using crossties featuring a 180° hook on the two ends. (b) The ductility of RC columns comprising lap-spliced crossties, crossties featuring a 180° hook on the two ends and conventional crossties under axial tension is superior to that under axial compression. (c) For RC columns under axial compression, when the axial force ratio is less than 30%, lap-spliced crossties can be used instead of conventional crossties. (d) The inner columns of the building structure are subjected to large axial compression. When the columns are only subjected to axial compression during the earthquake, and the column axial force ratio is greater than 30%, the use of lap-spliced crossties can not only meet the ACI design requirements, but also facilitate the construction. (e) When the columns are subjected to repeated axial forces (axial compression and axial tension) during the earthquake, generally speaking, the column axial force ratio in this case is less than 30%. In this case, lap-spliced crossties can be used to replace conventional crossties.
TitleLoad demand assessment of liquid storage tank in water supply facilities
AuthorYuan-Tao Weng, Gee-Yu Liu, Wen-Cheng Shen, Min-Lang Lin, Lap-Loi Chung, Chao- Hsien Li
Keywordswater supply facilities, seismic evaluation, liquid storage tank
AbstractWhen carrying out the seismic evaluation and analysis procedure of the liquid storage tank, the static load, live load, soil load, fluid load, temperature load and seismic load must be estimated first. The seismic load can be divided into earthquake-induced fluid dynamic load, dynamic load of the soil and the seismic force induced by the self-weight of the structure. Firstly, the dynamic load of the fluid caused by the earthquake can be further divided into the fluid impulsive modal load, the fluid convective modal load, and the horizontal dynamic load caused by the vertical vibration of the fluid. Secondly, the soil dynamic load caused earthquakes can also be divided into active soil pressure and passive soil pressure. In addition, the vertical seismic force of the liquid storage tank and the lateral inertial force of the tank wall should also be considered. This study focuses on load demand assessment methods and seismic evaluation process for the common pool-like water tank structure in Taiwan to make the seismic evaluation and analysis procedures more feasible and reasonable.
TitleSeismic Performance of Crossing–fault Bridges
AuthorHsiao-Hui Hung, Lian-Gui He, Yi-Che Ho, Ching-Chiang Chuang, Chang-Wei Huang
KeywordsCrossing-fault bridge, nonlinear time history, multiple excitation, ground displacement input
AbstractThe influences of near-fault earthquakes are taken into account only by the magnification factors in the seismic design code for highway bridges. There are no related specifications about crossing-fault bridges in the design code. However, cross-fault bridges which are subjected to different ground motions at opposite sides of the fault line suffer more attacks in earthquakes. In this study, the seismic responses of cross-fault bridges are simulated with the multiple-excitation method and solved by nonlinear dynamic time history analyses. The displacement time history of each excitation is obtained by integrating the acceleration time history of a near-fault ground motion. The influences of the velocity impulse and residual displacements of near-fault earthquakes on the seismic responses of cross-fault bridges are discussed. In addition, the effects of the boundary conditions of the bridge deck and the angle between the bridge and fault line on the seismic responses of cross-fault bridges are also elaborated here. Numerical results demonstrate that the multiple-excitation simulation obtained larger local deformation and internal forces. On the other hand, the single-excitation simulation obtained larger absolute acceleration. Moreover, the ground displacements from integration are further divided into absolute displacements and relative displacements, which are assigned to the ground motions at opposite sides of the fault line. Numerical results show that there are no obvious differences on internal forces between these two displacement distributions. However, the absolute displacement generates larger member deformation. Moreover, the torsions at the bottom of bridge columns are magnified when the fault angle is 45°. Finally, the influences of different boundary conditions between bridge slabs and columns on the seismic responses are investigated. The seismic responses of rigid connections are similar to those of pin connections while the seismic responses of simply supported bridges have different characteristics
TitleProbabilistic Assessment of Seismic Performance and Collapse Risk for Irregularly Bridge
AuthorKuang-Yen Liu, Yi-Han Lu
KeywordsScouring Effect, Soil Spring, Group Pile Effect, Probabilistic Assessment Method, Collapse Risk Analysis, Incremental Dynamic Analysis, Static Pushover Analysis
AbstractThis study investigates the seismic performance and collapse risk of a group pile foundation irregularly bridge after scouring, which use API soil spring method to build a group pile foundation, four-span bridge models, and use probabilistic assessment to discuss the seismic performance due to different scouring places. This methodology was presented by previous researcher. For numerical analysis, this study uses SAP2000 to do incremental dynamic analysis (IDA). Afterward, based on the result, also establish fragility curve considering IO, LS, and CP performance. This study also uses pushover analysis to evaluate the seismic performance of bridge after scouring. The result shows the first yielding point for group pile will appear at the top of the pile. Second, Seismic performance for the bridge will have the greatest influence when scouring was taken place at the pier which has the biggest stiffness difference compare to its nearby pier. Last, pushover analysis for irregularly bridge may underestimate its reaction compare to nonlinear time history analysis. All in all, this simplified probabilistic procedure can be used as a reference for future seismic performance evaluation for bridges.