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CONTENTS
Volume 8, Number 6, December 2008
 

Abstract
This paper presents an effective hysteretic model for the prediction and evaluation of steel reinforced concrete member seismic performance. This model adopts the load-deformation relationship acquired from monotonic load tests and incorporates the double-pivot behavior of composite members subjected to cyclic loads. Deterioration in member stiffness was accounted in the analytical model. The composite member performance assessment control parameters were calibrated from the test results. Comparisons between the cyclic load test results and analytical model validated the proposed method?s effectiveness.

Key Words
Steel reinforced concrete; seismic performance; assessment; hysteretic model

Address
Jia-Lin Juang and Hsieh-Lung Hsu : Dept. of Civil Engineering, National Central University, Chung-Li, Taiwan 32054

Abstract
Yielding of the internal steel reinforcement is an important mechanism that influences the Intermediate Crack-induced debonding (IC debonding) behavior in FRP-strengthened RC members since the FRP is required to carry additional forces beyond the condition of steel yielding. However, rational design practice dictates an appropriate limit state is defined when steel yielding is assured prior to FRP debonding. This paper proposes a criterion which correlates the occurrence of IC debonding to the formulation of a critical steel yielding length. Once this length is exceeded the average bond stress in the FRP/concrete interface exceeds its threshold value, which proves to correlate with the average bond resistance in an FRP/concrete joint under simple shear loading. This proposed IC debonding concept is based on traditional sections analysis which is conventionally applied in design practice. Hence complex bond stress-slip analyses are avoided. Furthermore, the proposed model incorporates not only the bond properties of FRP/concrete interface but also the beam geometry, and properties of steel and FRP reinforcement in the analysis of IC debonding strength. Based upon a solid database, the validity of the proposed simple IC debonding criterion is demonstrated.

Key Words
fiber reinforced plastics; reinforced concrete beams; flexural strengthening; IC debonding

Address
Jian-Guo Dai: Department of Civil and Structural Engineering, The Hong Kong Polytechnic University Hung Hom, Kowloon, Hong Kong
Kent A. Harries : Department of Civil and Environmental Engineering, University of Pittsburgh 936 Benedum Hall, Pittsburgh PA 15261, U.S.A
Hiroshi Yokota : Port and Airport Research Institute, Yokosuka 239-0826, Japan

Abstract
A hybrid tabu-simulated annealing algorithm is proposed for the optimum design of steel frames. The special character of the hybrid algorithm is that it exploits both tabu search and simulated annealing algorithms simultaneously to obtain near optimum. The objective of optimum design problem is to minimize the weight of steel frames under the actual design constraints of AISC-LRFD specification. The performance and reliability of the hybrid algorithm were compared with other algorithms such as tabu search, simulated annealing and genetic algorithm using benchmark examples. The comparisons showed that the hybrid algorithm results in lighter structures for the presented examples.

Key Words
optimum design; steel frames; tabu search; simulated annealing; hybrid heuristic algorithm

Address
S.O. Degertekin and M.S. Hayalioglu : Department of Civil Engineering, Dicle University, 21280, Diyarbakir, Turkey
M. Ulker : Department of Civil Engineering, Firat University, 23119, Elazig, Turkey

Abstract
This paper presents a plan and guidelines that were drawn for Korean based research carried out on the fire-resistance of CFT columns. This research was carried out by reviewing the Korean regulations related to the fire-resistance of CFT columns and examining studies which had been made in Korea as well as overseas. The first phase of the study plan was to compare the fire-resistance of square CFT columns without fire protection (obtained through fire-resistance tests and numerical analyses) with estimated values (obtained through fire-resistance design formulas proposed in Korea and overseas). This comparison provided conclusions as outlined below. Fire-resistance tests conducted in this study proved that, when the actual design load is taken into consideration, square CFT columns without fire protection are able to resist a fire for more than one hour. A comparison was made of test and analysis results with the fire-resistance time based on the AIJ code, the AISC design formula and the estimation formula suggested for Korea. The results of this comparison showed that the test and analysis results for specimens SAH1, SAH2-1, SAH2-2 and SAH3 were almost identical with the AIJ code, the AISC design formula and estimation formula. For specimens SAH4 and SAH5, the estimation formula was more conservative than the AIJ code and the AISC design formula. It was necessary to identify the factors that have an influence on the fire-resistance of CFT columns without fire protection and to draw fire-resistance design formulas for these columns. To achieve this, it is proposed that numerical analyses and tests be conducted in order to evaluate the fire-resistance of circular CFT columns, the influence of eccentricity existing as an additional factor and the influence of the slenderness ratio of the columns. It is also suggested that the overall behavior of CFT structures without fire protection within a fire be evaluated through analysis simulation.

Key Words
fire resistance; concrete-filled steel square tube column; without fire protection; constant central axial load; numerical analysis; fire-resistance test

Address
Su-Hee Park and Sung-Mo Choi : Department of Architectural Engineering, University of Seoul, Korea
Kyung-Soo Chung : Architectural Engineering Research Team, Research Institute of Industrial Science and Technology, Korea

Abstract
This paper discusses a feasibility of a new type of two-way system for single layer lattice domes with nodal eccentricity by investigating the dynamic behavior under earthquake motions. The proposed dome is composed of two main arches, intersecting each other with T-joint struts to provide space for tensioning membranes. The main purposes of this study are to calculate the nonlinear dynamic response under severe earthquake motions and to see the possibility of using this new type of two-way system for single layer lattice domes against earthquake motions. The results show that the main arches remain elastic except yielding of the joints of strut members that can be used to absorb some amount of strain energy at strong earthquake motion. Consequently, deformation of the main arches can be reduced and any heavy damages on the main arches can be minimized. A kind of damage-control characteristic appeared in this system may be utilized against severe earthquake motions, showing a possibility of designing a new type of single layer lattice dome.

Key Words
earthquake response; lattice dome; single layer; two-way; nodal eccentricity; damage controller

Address
Eka Satria, Shiro Kato, Shoji Nakazawa and Daisuke Kakuda : Dept. of Architecture and Civil Engineering, Toyohashi Univ. of Technology, Tempaku-cho Azahibarigaoka1-1, Toyohashi, 441-8580, Japan


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