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CONTENTS
Volume 49, Number 2, January25 2014
 

Abstract
In this paper a nonlinear finite element analysis model is established for cold-formed steel zed-section purlins subjected to uplift loading. In the model, the lateral and rotational restraints provided by the sheeting to the purlin are simplified as a lateral rigid restraint imposed at the upper flange-web junction and a rotational spring restraint applied at the mid of the upper flange where the sheeting is fixed. The analyses are performed by considering both geometrical and material nonlinearities. The influences of the rotational spring stiffness and initial geometrical imperfections on the uplift loading capacity of the purlin are investigated numerically. It is found that the rotational spring stiffness has significant influence on the purlin performance. However, the influence of the initial geometric imperfections on the purlin performance is found only in purlins of medium or long length with no or low rotational spring stiffness.

Key Words
zed-purlin; uplift; imperfection; nonlinear analysis; lateral-torsional buckling; moment capacity; finite element

Address
Jue Zhu, Jian-kang Chen : Faculty of Mechanical Engineering and Mechanics, Ningbo University, Ningbo, China
Chong Ren : School of Civil Engineering, University of Birmingham, Birmingham, UK

Abstract
Safety factors proposed in codes CEB, B.A.E.L 91 and EUROCODE 1 cover a great number of uncertainties; making them inadequate for the assessment of existing structures. Suitable safety factors are established using a probabilistic assessment, once real dimensions, materials strength and existing structures deterioration mechanisms are taken into account. This paper presents a calibration method for safety factors using a typical set of RC bridges in France. It considers the principal stages of corrosion provoked by CO2 and Cl− penetration and threshold indexes (B0) for existing structures. Reliability indexes are determined by the FORM method in the calibration method.

Key Words
calibration; corrosion; reinforced concrete; reliability; safety factors

Address
Rita C. Silva : Faculty UnB Gama, Complexo de Educacao, University of Brasilia, Cultura, Esporte e Lazer, 72405-610, Gama, Brazil
Christian Cremona : Directorate for Research and Innovation, Ministry of Ecology, Energy, Sustainable Development and Sea, Tour Pascal, 92055 La Defense, France

Abstract
A new method of multiple damage detection in beam like structures is introduced. The mode shapes of both healthy and damaged structures are used in damage detection process (DDP). Multiple Damage Localization Index Based on Mode Shapes (MDLIBMS) is presented as a criterion in detecting damaged elements. A finite element modeling of structures is used to calculate the mode shapes parameters. The main advantages of the proposed method are its simplicity, flexibility on the number of elements and so the accuracy of the damage(s) position(s), sensitivity to small damage extend, capability in prediction of required number of mode shapes and low sensitivity to noisy data. In fact, because of differential and comparative form of MDLIBMS, using noise polluted data doesn\'t have major effect on the results. This makes the proposed method a powerful one in damage detection according to measured mode shape data. Because of its flexibility, damage detection process in multi span bridge girders with non-prismatic sections can be done by this method. Numerical simulations used to demonstrate these advantages.

Key Words
structural damage detection; Multiple Damage Localization Index Based on Mode Shapes (MDLIBMS); Finite element modeling; Damage detection process (DDP)

Address
F. Homaei, G. Ghodrati Amiri : School of Civil Engineering, Iran University of Science & Technology, Tehran, Iran
S. Shojaee : Department of Civil Engineering, Shahid Bahonar University, Kerman, Iran

Abstract
The extensive use of prestressed reinforced concrete (PSC) highway bridges in marine environment drastically increases the sensitivity to both fatigue- and corrosion-induced damage of their critical structural components during their service lives. Within this scenario, an integrated method that is capable of evaluating the fatigue reliability, identifying a condition-based maintenance, and predicting the remaining service life of its critical components is therefore needed. To accomplish this goal, a procedure for fatigue reliability prediction of PSC highway bridges is proposed in the present study. Vehicle-bridge coupling vibration analysis is performed for obtaining the equivalent moment ranges of critical section of bridges under typical fatigue truck models. Three-dimensional nonlinear mathematical models of fatigue trucks are simplified as an eleven-degree-of-freedom system. Road surface roughness is simulated as zero-mean stationary Gaussian random processes using the trigonometric series method. The time-dependent stress-concentration factors of reinforcing bars and prestressing tendons are accounted for more accurate stress ranges determination. The limit state functions are constructed according to the Miner\'s linear damage rule, the time-dependent S-N curves of prestressing tendons and the site-specific stress cycle prediction. The effectiveness of the methodology framework is demonstrated to a T-type simple supported multi-girder bridge for fatigue reliability evaluation.

Key Words
corrosion-fatigue;vehicle-bridge coupling vibration;reliability assessment;prestressed reinforced concrete bridge

Address
Jinsong Zhu: Key Laboratory of Coast Civil Structure Safety, Ministry of Education, Tianjin University, Tianjin 300072, People\'s Republic of China; School of Engineering, San Francisco State University, San Francisco, CA 94132, USA
Cheng Chen: School of Engineering, San Francisco State University, San Francisco, CA 94132, USA
Qinghua Han: 3School of Civil Engineering, Tianjin University, Tianjin 300072, People\'s Republic of China

Abstract
Cold expansion is an efficient way to improve the fatigue life of an open hole. In this paper, three finite element models have been established to bind the crack growth from an expanded hole and simulated. Expansion and its degree influence are studied using a numerical analysis. Stress intensity factors are determined and used to evaluate the fatigue life. Residual stress field is evaluated using a nonlinear analysis and superposed with the applied stresses field in order to estimate fatigue crack growth. Experimental tests are conducted under constant loading. Results of this investigation indicate expansion and its degree are beneficial to fatigue life and a good agreement was observed between FEM simulations and experimental results.

Key Words
crack growth; cold expansion; residual stress; finite element method; fatigue life

Address
Abdekrim Aid, Zahar Semari : Laboratoire LPQ3M, Universite de Mascara, B.P 305, Mascara, 29000, Algeria
Mohamed Benguediab : Departement de Genie Mecanique, Universite de Sidi-Bel-Abbes, Algeria

Abstract
Wind-induced failure around screwed connections has been documented in roof and wall cladding systems made with steel sheet cold-formed panels during high wind events. Previous research has found that low cycle fatigue caused by stress concentration and fluctuating wind loads is responsible for most such failures. A dynamic load protocol was employed in this work to represent fatigue under wind effects. A finite element model and fatigue criteria were implemented and compared with laboratory experiments in order to predict the fatigue failure associated with fluctuating wind loads. Results are used to develop an analytical model which can be employed for the fatigue analysis of steel cold-formed cladding systems. Existing three dimensional fatigue criteria are implemented and correlated with fatigue damage observed on steel claddings. Parametric studies are used to formulate suitable yet simple fatigue criteria. Fatigue failure is predicted in different configurations of loads, types of connections, and thicknesses of steel folded plate cladding. The analytical model, which correlated with experimental results reported in a companion paper, was validated for the fatigue life prediction and failure mechanism of different connection types and thicknesses of cold-formed steel cladding.

Key Words
cold-formed plates; connections; dynamic load protocol; fatigue failure; finite element analysis; folded plates; steel; wind

Address
Osvaldo Rosario-Galanes : Department of Civil Engineering, University of Puerto Rico, Mayaguez, Puerto Rico
Luis A. Godoy : Structures Department, FCEFyN, National University of Cordoba, and CONICET, P.O. Box 916, Cordoba 5000, Argentina

Abstract
This paper reported an experimental study on creep behaviors of PVB and Ionoplast laminated glass (LG) under load duration of 30 days. The tests were carried out in room temperature (23\'C). The study revealed that after sustaining loads for 30 days, the mid-span deflection of PVB LG increased by almost 102% compared with its short term deflection, while that of Ionoplast LG approximately increased by 14%; composite effects between two glass plies in PVB LG gradually reduced with time, but did not fully vanish at the 30th day; two glass plies in Ionoplast LG on the other hand was able to withstand loads as an effective composite section during the entire loading period; the creep behaviors of both LG were not finished yet at the 30th day. In addition to this, also studied was the varying of the bending stresses of PVB and Ionoplast LG under load duration of 2 hours. The tests were carried out in ambient temperatures of 30\'C, 50\'C and 80\'C respectively. It was found that under a given load, although the bending stresses of both LG increased with increasing temperature, for PVB LG the increasing rate of the bending stress decreased with increasing temperature, while for Ionoplast LG the increasing rate of the bending stress increased with increasing temperature.

Key Words
PVB laminated glass; Ionoplast laminated glass; long duration load; temperature; creep; four-point bending

Address
Xiaokun Huang, Gang Liu, Qiang Liu : Research and Development, China Academy of Building Research, Beijing 100013, China
Stephen J. Bennison : E.I. DuPont de Nemours & Co. Inc., USA

Abstract
According to deformation features of pre-twisted bar, its elastic bending and torsion buckling equation is developed in the paper. The equation indicates that the bending buckling deformations in two main bending directions are coupled with each other, bending and twist buckling deformations are coupled with each other as well. However, for pre-twisted bar with dual-axis symmetry cross-section, bending buckling deformations are independent to the twist buckling deformation. The research indicates that the elastic torsion buckling load is not related to the pre-twisted angle, and equals to the torsion buckling load of the straight bar. Finite element analysis to pre-twisted bar with different pre-twisted angle is performed , the prediction shows that the assumption of a plane elastic bending buckling deformation curve proposed in previous literature (Shadnam and Abbasnia 2002) may not be accurate, and the curve deviates more from a plane with increasing of the pre-twisting angle. Finally, the parameters analysis is carried out to obtain the relationships between elastic bending buckling critical capacity, the effect of different pre-twisted angles and bending rigidity ratios are studied. The numerical results show that the existence of the pre-twisted angle leads to \"resistance\" effect of the stronger axis on buckling deformation, and enhances the elastic bending buckling critical capacity. It is noted that the \"resistance\" is getting stronger and the elastic buckling capacity is higher as the cross section bending rigidity ratio increases.

Key Words
pre-twisted bar; flexural buckling; torsional buckling; coupling; finite element

Address
Chang Hong Chen and Yao Yao: School of Mechanics and Civil Engineering, Northwestern Polytechnical University, Xi\'an 710072, China
Ying Huang: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China


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