Parametric study on dynamic interaction of horizontally curved twin I-girder bridges and a moving vehicle

Behavior of horizontally curved I-girder bridges are complex and its interaction analysis is difficult. In this study, extended three-dimensional finite element interaction analyses were conducted parametrically. The bridge is modeled in detailed with solid and shell elements and vehicle is simulated as a nonlinear model according to HS20-44 design truck. Road roughness profiles are generated from power spectral density and cross spectral functions. By using these models, natural vibration and forced vibration analyses carried out in parametric study, are extensively investigated. The analytical results are significant and give some useful information regarding the impact factor of the studied bridge which could be much helpful for practical designer

Seismic Shear Forces in Shear Walls of a Medium-Rise Building Designed by Response Spectrum Analysis

According to ASCE7-05, response spectrum analysis (RSA) procedure can be used to determine the seismic demands of the structures for the seismic design of any type of structures. However, this design procedure has been found to be inappropriate for medium-rise and high-rise buildings. This paper is aimed at verifying the RSA procedure prescribed in the current Thai seismic design code which is based on ASCE7-05 and proposing appropriate modification to the design shear force from RSA procedure. A 16-story medium-rise reinforced-concrete core-wall case-study building was first designed based on RSA procedure and then the non-linear response history analysis (NLRHA) was performed to determine the more accurate seismic demands of the structure. The results show that seismic shear demand of the shear wall from non-linear analysis is about 2 times the shear capacity of the wall designed by RSA procedure. This could lead to shear failure in the shear walls designed by RSA procedure. To avoid shear failure in the shear wall elements, the shear demands in the wall elements designed by RSA procedure needs to be amplified by a factor of 2, which is equivalent to reducing the response modification factor R = 5.5 in ASCE7-05 to R = 2.75 (for shear force in the shear wall only)

SEISMIC RESPONSE OF CURVED GRILLAGE GIRDER VIADUCTS WITH BASE ISOLATION SYSTEM IN COLD REGION

The Thirteenth East Asia-Pacific Conference on Structural Engineering and Construction (EASEC-13), September 11-13, 2013, Sapporo, Japan

Bearing properties of Shorea obtusa beneath a laterally loaded bolt

Empirical equations to determine the bearing strength have been proposed by many researchers and design standards. Because these equations have been developed mainly based on test results of softwood species, it is a matter of great importance (to ASEAN structural engineers) to verify the applicability of these equations for tropical hardwood species, which are commonly used in many ASEAN countries. In this study, wood specimens of Shorea obtusa (a tropical hardwood species) were used and the bearing test under full-hole confi guration was carried out for fi ve different loading angles to the grain. The bearing stress-embedment curve obtained from the test was approximated by a linear elastic-plastic diagram indicating the initial and fi nal stiffness of the curve. Testing showed that the average bearing strength parallel to the grain was 7.25% lower than the prediction given in Eurocode 5. The bearing strength perpendicular to the grain evaluated based on bearing load at initial cracking was substantially different from any predictions given by previous studies or design standards. It was also found that the bearing strength and initial stiffness from the bearing stress-embedment curve for loading at intermediate angles to the grain could be satisfactorily predicted with Hankinson’s formula

Uniaxial tension-compression fatigue behavior and fiber bridging degradation of strain hardening fiber reinforced cementitious composites

This study aims to clarify experimentally the uniaxial tension-compression fatigue behavior and fiber bridging stress degradation of strain hardening fiber reinforced cementitious composites. During fatigue cyclic loading, tensile bridging stress corresponding to the preset maximum tensile strain was recorded with the number of cycles in order to observe the degradation of the tensile bridging stress. Major bridging stress degradation was observed before reaching 1,000 cycles, and microscopic observation of the failure surface confirmed severe fiber damages. Fitting curves of bridging stress degradation are proposed with the idea of Weibull distribution. The preliminary results of the current study with a limited number of specimens are compared with those of a uniaxial tensile fatigue study, and the differences of bridging stress degradations are discussed

Seismic response of highway viaducts equipped with lead-rubber bearings under low temperature

Based on a FEM based nonlinear dynamic numerical method, this study investigates the detrimental effects of low temperature on the seismic responses of a highway viaduct equipped with Lead-Rubber Bearings (LRBs). In this method, a dynamic bearing property definition is introduced to account for the temperature variation caused by the absorbed earthquake energy and the corresponding property variation of LRBs. Under low temperature conditions, the base isolation effect of LRBs which are well-designed for room temperature is significantly weakened, manifested by shorter fundamental structural natural periods and more damages and forces imposed to structure members, such as a 5-13% increment of shear force transferred by the LRBs, an increasing area of the hysteresis loop of the bending moment at the bottom of piers, and an increasing residual displacement at the top of piers. In addition, through jointed investigating the seismic responses under both long and short durations of earthquake motions, it is demonstrated that the heat production in LRBs over an earthquake can alleviate the detrimental effect of low temperature, and the extent of this alleviation is positively correlated to the earthquake duration. Therefore, the low temperature effect and the property variation of LRBs over an earthquake should be comprehensively considered for the designation of LRBs installed in bridge viaducts located in cold regions and the realization of an accurate seismic analysis of the bridge viaducts