Flexural retrofit of a bridge subjected to overweight trucks using CFRP laminates

The reinforced concrete spans of a bridge subjected to extreme vehicular loads are investigated and retrofitted with carbon fiber reinforced polymer (CFRP) laminates. A finite element model of the bridge superstructure was created to determine the forces resulting from extreme loads. A moment–curvature analysis was subsequently carried out to investigate the flexural characteristics of the reinforced concrete sections prior to and after strengthening with CFRP laminates. The analytical modeling concluded that significant strength can be gained at the ultimate limit state, while relatively small increase in strength is observed at service load levels. The increase in flexural resistance at ultimate does provide an adequate margin of safety against further overloading. The analytical investigation and the retrofitting work are presented herein.     

索承式桥梁吊索钢丝腐蚀疲劳寿命评估

根据吊索镀锌钢丝腐蚀疲劳破坏特点,把镀锌钢丝腐蚀疲劳纹形成和扩展过程分解成镀锌层腐蚀失效、蚀坑萌生、蚀坑形成、短裂纹扩展、长裂纹扩展和断裂破坏等阶段,建立各阶段时间表达式,得到镀锌钢丝疲劳寿命表达式,提出基于断裂力学的吊索钢丝腐蚀疲劳寿命评估研究结果方法。通过算例分析复杂运营条件下腐蚀环境和应力幅等因素对吊索钢丝腐蚀疲劳寿命的影响,研究结果表明：吊索钢丝腐蚀疲劳寿命主要由钢丝镀锌层腐蚀、蚀坑发展和短裂纹扩展等3个阶段组成,为了准确地评估吊索腐蚀疲劳寿命,需要掌握大桥的运营环境和交通荷载。     

铅阻尼器对网壳结构地震倒塌影响分析

综合考虑网壳结构杆件的失稳与失效,利用ANSYS/LS-DYNA软件建立网壳结构的数值模型,分析判别了网壳结构在强震作用下的倒塌破坏模式,包括动力强度破坏、动力失稳破坏和综合破坏三个类型.接着将铅阻尼器以能量等效的原则加入到网壳结构中,在三条不同地震波激励的情况下,分析了铅阻尼器减振系统对网壳结构倒塌模式的影响.结果证实:加入铅阻尼器减振系统之后,网壳结构的倒塌临界荷载被提高了1.11倍,同时网壳结构中的屈服杆件比例提高了3.29倍,与未加铅阻尼器减振系统的情况相比,网壳结构更倾向于发生动力强度破坏.     

Computational Parametric Analysis of Cellular Solids with the Miura-Ori Metamaterial Geometry under Quasistatic Compressive Loads

Origami-based metamaterials have widespread application prospects in various industries including aerospace, automotive, flexible electronics, and civil engineering structures. Among the wide range of origami patterns, the fourfold tessellation known as Miura-ori is of particular attraction to engineers and designers. More specifically, researchers have proposed different 3D structures and metamaterials based on the geometric characteristics of this classic origami pattern. Herein, a computational modeling approach for the design and evaluation of 3D cellular solids with the Miura-ori metamaterial geometry which can be of zero or nonzero thicknesses is presented. To this end, first, a range of design alternatives generated based on a numerical parametric model is designed. Next, their mechanical properties and failure behavior under quasistatic axial compressive loads along three perpendicular directions are analyzed. Then, the effects of various geometric parameters on their energy absorption behavior under compression in the most appropriate direction are investigated. The findings of this study provide a basis for future experimental investigations and the potential application of such cellular solids for energy-absorbing purposes.     

Estimating extreme temperature differences in steel box girder using long-term measurement data

The extreme temperature differences in fiat steel box girder of a cable-stayed bridge were studied.Firstly,by using the long-term measurement data collected by the structural health monitoring system installed on the Runyang Cable-stayed Bridge,the daily variations as well as seasonal ones of measured temperature differences in the box girder cross-section area were summarized.The probability distribution models of temperature differences were further established and the extreme temperature differences were estimated with a return period of 100 years.Finally,the temperature difference models in cross-section area were proposed for bridge thermal design.The results show that horizontal temperature differences in top plate and vertical temperature differences between top plate and bottom plate are considerable.All the positive and negative temperature differences can be described by the weighted sum of two Weibull distributions.The maximum positive and negative horizontal temperature differences in top plate are 10.30 ℃ and -13.80 ℃,respectively.And the maximum positive and negative vertical temperature differences between top plate and bottom plate are 17.30 ℃ and-3.70 ℃,respectively.For bridge thermal design,there are two vertical temperature difference models between top plate and bottom plate,and six horizontal temperature difference models in top plate.     

Experimental and computational investigations on fire resistance of GFRP composite for building façade

Composite materials such as glass fibre reinforced polymers (GFRPs) possess the advantages of high strength and stiffness, as well as low density and highly flexible tailoring; therefore, their potential in replacing conventional materials (such as concrete, aluminium and steel) in building façade has become attractive. This paper addresses one of the major issues that hinder the extensive use of composite structures in the high-rise building industry, which is the fire resistance. In this study, a fire performance enhancement strategy for multilayer composite sandwich panels, which are comprised of GFRP composite facets and polyethylene foam core, is proposed with the addition of environmentally friendly, fire retardant unsaturated polyester resins and gel-coats. A series of burning experimental studies including thermo-gravimetric analysis (TGA) and single burning item (SBI) are carried out on the full scale composite sandwich as well as on single constituents, providing information regarding heat release rate, total heat release, fire growth rate, and smoke production. Experimental results are compared with fire safety codes for building materials to identify the key areas for improvements. A fire dynamic numerical model has been developed in this work using the Fire Dynamics Simulator (FDS) to simulate the burning process of composite structures in the SBI test. Numerical results of heat production and growth rate are presented in comparison with experimental observations validating the computational model and provide further insights into the fire resisting process. Parametric studies are conducted to investigate the effect of fire retardant additives on the fire performance of the composite sandwich panel leading to optimum designs for the sandwich panel.     

Ferritic stainless steels in structural applications

Ferritic stainless steels are low cost, price-stable, corrosion-resistant materials. Although widely used in the automotive and domestic appliance sectors, structural applications are scarce owing to a dearth of performance data and design guidance. The characteristics of ferritics make them appropriate for structures requiring strong and moderately durable structural elements with attractive metallic surface finishes. The present paper provides an overview of the structural behaviour of ferritic stainless steels, including a summary of the findings of a recent European project (SAFSS) on ferritics. Laboratory experiments have been completed including material tests as well as structural member tests, both at ambient and elevated temperatures. The experimental data is supplemented by numerical analysis in order to study a wide range of parameters. The findings of this work have enabled design guidance to be proposed, as discussed herein.     

Guidelines for flexural resistance of FRP reinforced concrete slabs and beams in fire

Several building codes are currently available for the design of concrete structures reinforced with fiber-reinforced polymer (FRP) bars. Nevertheless, there is little information provided about structural behavior in case of fire and no reliable design methods are available for FRP reinforced concrete (RC) members in fire. The goal of this paper is to provide guidelines for the calculation of the resistant bending moment of FRP-RC members exposed to fire in compliance with the provisions of Eurocodes, based on studies recently carried out by the authors. The paper provides a conceptual approach to fire safety checks for bending moment resistance of FRP-RC members. With reference to thermo-mechanical analysis, a simplified design method (for both thermal and mechanical analyses) for sagging bending moment resistance of FRP-RC slabs in fire situations is finally suggested.     

Bond between FRP composites and concrete: Assessment of design procedures and analytical models

The use of fibre reinforced polymers (FRPs) to strengthen reinforced concrete (RC) structures has gained a wide popularity in the last decades. Although many experimental and analytical studies are available in literature, some issues are still under discussion in the research communities. Since the typical failure mode of FRP–concrete joints is reported to be debonding of the composite from the concrete substrate [1], the estimation of the bond strength between FRP and concrete substrate represents a key issue for the proper use of this technology. For this reason, several analytical models for the evaluation of the FRP–concrete bond strength and few models for the estimation of the effective bond length were proposed (some of them are included in design codes/recommendations/guidelines); however they were not assessed by means of an appropriate experimental database.This work shows an assessment of twenty analytical models for the evaluation of the FRP–concrete bond strength. The assessment is based on the analysis of a wide experimental database collected from the literature. The results are provided distinguishing between the test setup adopted (single or double shear test, bending test) and the material used (post impregnated sheets or pre impregnated laminates). The accuracy of each model was evaluated by means of a simplified statistical analysis. The influence of the test setup and basic material on the accuracy of the model used was analysed as well. Lastly, the accuracy of twelve available models in providing an estimation of the effective bond length was also assessed.     

Characterisation of the mechanical properties of pultruded fibre-reinforced polymer tube

This paper presents an investigation on the mechanical properties of pultruded fibre-reinforced polymer (FRP) tube. Unlike typical FRP tube, the investigated tube has additional ±45° glass fibre reinforcement making it suitable for several structural applications. Tests on coupons and full-scale specimens were undertaken to determine the mechanical properties of the tube. Moreover, a finite element (FE) analysis was carried to simulate the compressive and flexural behaviours of full-scale specimen. Experimental results showed that coupon and full-scale specimens exhibited linearly elastic up to failure. The maximum variation of the experimental data is up to 8% indicating that the reproducibility of the test is quite reasonable and that the experimental procedures were conducted within the acceptable margin of error. The comparison between the compressive and flexural peak load values obtained experiment and FE methods revealed that their difference is less than 5%. Furthermore, the compressive and flexure failure modes obtained from the experiment were fairly simulated in the FE analysis. These indicated that FE analysis predicted reasonably the actual compressive and flexural behaviours of the pultruded FRP tube.