Vol.33/No.4 (132) (2018)

作者:

Vol.33/No.4 (132) (2018)

Title Strongback systems for enhancing the seismic performance of buildings
Author Meng-Kwee Kek, Jui-Liang Lin, Keh-Chyuan Tsai
Keywords inter-story drift ratio, generalized building model, strongback, nonlinear response history analysis
Abstract In order to reduce the variations of peak inter-story drifts occurred in earthquakes along the building height, this research conducts the parametric study of the buildings with strongback systems through simplified numerical models. The generalized building model (GBM) and generalized building model with strongback (GBMSB) are employed as the simplified numerical models in the parametric study. This study investigated 3, 6, 9 and 20-story buildings.The peak inter-story drift ratios along the building height are computed by using the response spectrum analysis method, in which the peak modal responses are combined according to the SRSS method. The optimization objective is to minimize the standard deviation of the peak inter-story drift ratios. The optimal stiffness distribution of a strongback is thus obtained.The results of parametric study show that when a pure shear-type strongback, whose first story is stiffened and its story stiffness decreases linearly along the height, the standard deviation of inter-story drifts is minimized. The effectiveness of the proposed method is verified by investigating one 9-story steel building and one 3-story reinforced concrete (RC) building.The 9-story steel moment resisting frame, designated as SAC9, was a prototype building located in Los Angeles adopted in SAC steel research project. In addition, the 3-story RC building, designated as T3,was tested using shaking table at Tainan Laboratory of National Center for Research on Earthquake Engineering. The optimal designs of SAC9 and T3 with the strongbacks are designated as SAC9-SB and T3-SB, respectively. Nonlinear response history analyses (NRHA) of SAC9, T3, SAC9-SB, T3-SB models and the others with different properties of strongback systems were conducted using PISD3D program. The NRHA result shows that SAC9-SB and T3-SB have smaller standard deviations than those using other strongback properties. The analysis results confirm the effectiveness of the proposed method in proportioning the strongback for buildings.
Title Fracture Tests and Finite Element Analysis of Diaphragm Connection in Steel Beam-to-Box Column Joints
Author Chung-Che Wu, Chao-Hsien Li, Ching-Yi Tsai, Ker-Chun Lin, Sheng-Jhih Jhuang, Keh-Chyuan Tsai
Keywords steel box column, electro-slag welding, heat affected zone, fracture prediction model, steel beam-to-box column connection, finite element model analysis, circumferential notched tensile test, ultrasonic test
Abstract Steel box columns are widely used in steel building structures in Taiwan due to the strong axes in two directions. In order to transfer the beam end moment to column, diaphragm plates of the same thickness and elevations as beam flanges are usually welded inside box column. Electro-slag welding (ESW) process is typically used in attaching the diaphragms to column flanges. This ESW process has been widely used in steel beam-to-box column joints in Taiwan because of its’ convenience and efficiency. However, ESW may increase the hardness of the welds and heat affected zones (HAZs), while reduce the Charpy-V Notch (CVN) strength in HAZ. This situation could cause the diaphragm to column flange weld to suffer premature fracture before a large plastic rotation is developed in beam-to-box column joints. In order to quantify the critical eccentricity and the effectiveness of predicting the fractures, this study utilizes the fracture prediction model and finite element model (FEM) analysis to correlate the test results. In this study, three beam-to-box column connection subassembly tests have been conducted with a different loading protocol or the shape of ESW chamber. Test results show that the fracture instances can be predicted based on the cumulative plastic deformation in the HAZs. Tests confirm that the possible fracture of the diaphragm to column flange welds can be mitigated by enlarging the chamber of the ESW. When the fracture prediction model is applied, the material parameters were firstly established from the Circumferential Notched Tensile (CNT) tests and FEM analysis. Subsequently, these parameters were used to predict the fractures observed in the ESW component tests and beam-to-box column connection subassembly tests. The fracture locations and instances can be reasonably well predicted by a suitable FEM model analysis. Thus, the effectiveness of CNT and the fracture model are confirmed. Analytical results also show fracture instances and locations are sensitive to the relative locations of the ESW and the beam flange. Thus, the importance of ultrasonic test in assuring the quality of the ESW is evident.
Title Life-cycle Cost Assessment Method Development for Steel Bridges Considering the Effect of the Renewal Periods of Coating Systems
Author C. K. Chiu, C. C. Chen, M. Y. Chen
Keywords steel bridge, deterioration rate, life-cycle maintenance cost, anti-corrosion coating system
Abstract In the maintenance stage of steel bridges, the costs can be divided into the regular maintenance cost and anti-corrosion coating cost. For the regular maintenance cost, this work adopts the Bayesian updating to determine the deterioration rate of each component or member. Additionally, based on the minimal regular maintenance cost, the corresponding maintenance period can be obtained. In order to quantify the renewal cost of the anti-corrosion coating system, this work conducts the accelerated-weathering test and site exposure test for the anti-corrosion coating materials. In addition to the testing results, the past investigations on the consuming rates of the specified coating materials for steel bridges are referred to determine the renewal periods of the anti-corrosion coating system. Finally, an assessment method of the life-cycle cost (LCC) of steel bridges is developed to investigate effect of the renewal period of the anti-corrosion coating system on the LCCs for 26 steel bridges located in a special municipality in Taiwan.
Title Capacity-Based Inelastic Displacement Spectra for Seismic Design and Evaluation of Reinforced Concrete Bridges
Author Ping-Hsiung Wang, Kuo-Chun Chang, Yu-Chen Ou
Keywords spectrum, inelastic displacement ratio, damage index, smooth hysteretic model, far-field earthquake, near-fault earthquake, seismic design and evaluation, RC bridges
Abstract Capacity-based inelastic displacement spectra that comprised an inelastic displacement (CR) spectrum and a corresponding damage state (DI) spectrum was proposed in this study to aid seismic evaluation and design of reinforced concrete (RC) bridges. Nonlinear time history analyses of SDOF systems were conducted using a versatile smooth hysteretic model that accounted for the influences of various column design parameters when subjected to far-field and near-fault ground motions. It was proved that the Park and Ang’s damage index not only can be used to accurately predict the onset of strength deterioration, but also can be a good indicator for assessing the actual visible damage condition of column regardless of its loading history, providing a better insight into the seismic performance of bridges. The computed spectra show that the CR for far-field ground motions approximately conforms to the equal displacement rule for structural period (Tn) larger than around 0.8 seconds, but that for near-fault ground motions departs from the rule in the whole spectral regions. Moreover, the near-fault ground motions would lead to significantly greater CR and DI than far-field ground motions and most of the design scenarios investigated in this research cannot survive the near-fault ground motions when relative strength ratio R = 5.0. Based on the computed spectra, CR and DI formulae are presented as a function of Tn, R, and various design parameters for far-field and near-fault ground motions. Finally, application of the proposed spectra to the performance-based seismic design and evaluation of RC bridge was presented using DI as the performance objective.
Title Estimation of Design Pressure Coefficient Based on Extreme Value Analysis Theory
Author Yuan-Lung Lo, Michael Kasperski
Keywords Design wind speed, Extreme value distribution, Pressure coefficient, Optimal design fractile
Abstract To determine a proper design wind load relies on correct evaluations on design wind speed and design wind pressure coefficient. The evaluation on design wind speed requires the understanding of local meteorological information accumulated for a long-term period and the knowledge of extreme value analysis; wind pressure coefficient of the target structure can be obtained via properly arranged wind tunnel test fulfilling the satisfactory demand of all non-dimensional aerodynamic parameters. By satisfying the target exceedance probability of failure of a target building, convolution process of probability densities of design wind speed and pressure coefficients is carried out and then the optimal design pressure coefficient can be found through iterative calculation. This study intends to apply local meteorological information in Taiwan and a simple wind tunnel test to demonstrate the determination of the optimal design fractile and its corresponding design wind pressure coefficient and design wind load.