Evaluating long-term benefits of geosynthetics in flexible pavements built over weak subgrades by finite element and Mechanistic-Empirical analyses

Finite element (FE) models were developed to evaluate the benefits of geosynthetic reinforcement in flexible pavements built over weak subgrades. The parametric study was conducted to evaluate the effect of different variables such as base thickness, geosynthetic type, geosynthetic stiffness, and double-geogrid layers. FE analyses were performed for 100 load cycles, and the permanent deformation (PD) was used to calibrate the empirical parameters in MEPDG equations for each layer, which were used to extrapolate PD data for the service life of pavements. The PD curves for unreinforced and similar reinforced sections were used to evaluate the Traffic Benefit Ratios (TBR) at different rut depths. The results showed that the inclusion of one geogrid/geotextile layer at the base-subgrade interface could significantly reduce pavement rutting. The use of geogrid is more effective than geotextile in reducing pavement rutting. The derived TBR values range from 1.91 to 8.9 for one geogrid layer and from 1.71 to 5.92 for one geotextile layer. The TBR values increase with increasing the rutting depth and geosynthetic stiffness. The TBR value demonstrates an optimum at a base thickness of 10 in. The results demonstrated the superior benefits of using double geogrid layers compared to single-layer cases.     

Seismic performance of MR frames protected by viscous or hysteretic dampers

This study concerns the behaviour of steel frames protected by different anti‐seismic devices (dampers). Typical hysteretic and viscous dampers are arranged in three steel moment‐resisting frames (MRFs) having different dynamical features but are designed to accomplish determined performance objectives. The proposed devices are selected following an iterative procedure based on the use of a suitable damage functional, which has been applied to control the behaviour of the protected structures under a specific seismic record. The outcomes obtained by implementing incremental dynamic analyses, carried out on the basis of seven historical records characterized by different features, allow to analyse the improvement of the structural performance due to the considered dampers and, therefore, to provide design information about their employment. The comparison of results is carried out taking into account the dampers capacity to protect the structures from damage, the inter‐storey drifts, the residual deformations and the possible amplification effects. In conclusion, the equivalent behaviour factors for each damper type are given, with the aim of providing useful design parameters for the implementation of simplified conventional linear analyses. Copyright © 2014 John Wiley & Sons, Ltd.     

Response surface‐based finite‐element model updating of a historic masonry minaret for operational modal analysis

This study aimed to use the response surface (RS) method for finite element (FE) model updating, using operational modal analysis (OMA). The RS method was utilized to achieve better agreement between the numerical and field‐measured structure response. The OMA technique for the field study was utilized to obtain modal parameters of the selected historic masonry minaret. The natural frequencies and mode shapes were experimentally determined by the enhanced frequency domain decomposition (EFDD) method. The optimum results between the experimental and numerical analyses were found by using the optimization method. The central composite design was used to construct the design of experiments, and the genetic aggregation approach was performed to generate the RS models. After obtaining the RS models, an attempt was made to converge the natural frequency values corresponding to the five‐mode shapes with the frequency values identified by the experimental analysis. ANSYS software was used to perform 3D finite element (FE) modeling of the historic masonry minaret and to numerically identify the natural frequencies and mode shapes of the minaret. The results of the experimental, initial, and updated FE model were compared with each other. Significant differences can be seen when comparing the experimental and analytical results with the initial conditions.     

粘钢加固对简支T型梁桥动力特性的影响

以福建安溪清溪大桥为工程背景,首先进行了粘钢加固前后的环境振动测试和刹车等强迫振动测试,并进行了实验模态分析;其次,分别建立了粘钢加固前后全桥的有限元模型,进行了模型参数修正,并比较了加固前后桥梁动力特性的变化;最后,基于修正后的模型,考察了粘贴钢板厚度和高度、T梁横向联结程度、桥面铺装厚度以及主梁腹板损伤程度等参数对粘钢维修加固桥梁动力特性的影响。结果表明:清溪大桥加固前后动力特性测试和分析结果基本吻合,粘钢加固改造能有效提高桥梁的振动频率和整体刚度。     

Numerical evaluation of the performance of a Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) under different loading conditions

This paper presents the results of a finite element (FE) numerical analysis that was developed to simulate the fully-instrumented Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) at the Maree Michel Bridge in Louisiana. Four different loading conditions were considered in this paper to evaluate the performance of GRS-IBS abutment due to dead loading, tandem axle truck loading, service loading, and abnormal loading. The two-dimensional FE computer program PLAXIS 2D 2016 was selected to model the GRS-IBS abutment. The hardening soil model proposed by Schanz et al., (1999) that was initially introduced by Duncan and Chang (1970) was used to simulate the granular backfill materials; a linear-elastic model with Mohr-Coulomb frictional criterion was used to simulate the interface between the geosynthetic and backfill material. Both the geosynthetic and the facing block were modeled using linear elastic model. The Mohr-Coulomb constitutive model was used to simulate the foundation soil. The FE numerical results were compared with the field measurements of monitoring program, in which a good agreement was obtained between the FE numerical results and the field measurements. The range of maximum reinforcement strain was between 0.4% and 1.5%, depending on the location of the reinforcement layer and the loading condition. The maximum lateral deformation at the face was between 2 and 9 mm (0.08%–0.4% lateral strain), depending on the loading condition. The maximum settlement of the GRS-IBS under service loading was 10 mm (0.3% vertical strain), which is about two times the field measurements (～5 mm). This is most probably due to the behavior of over consolidated soil caused by the old bridge. The axial reinforcement force predicted by FHWA (Adams et al., 2011b) design methods were 1.5–2.5 times higher than those predicted by the FE analysis and the field measurements, depending on the loading condition and reinforcement location. However, the interface shear strength between the reinforcement and the backfill materials predicted by Mohr-Coulomb method was very close to those predicted by the FE.     

在役T构桥梁的有限元模型修正

有限元模型修正是建立精确的基准有限元模型的基础。以在役T构桥梁——324国道乌龙江大桥为工程背景,利用ANSYS软件建立了全桥结构的三维有限元模型,进行了结构静、动力数值模拟分析,并与实测结果进行了比较;结果表明,未修正的有限元模型计算结果与实测结果存在较大误差。通过参数灵敏度分析,确定了对桥梁结构静、动力特性影响均较大的参数;采用零阶和一阶算法,基于自振频率与静力挠度组合的目标函数,对乌龙江大桥有限元模型进行了修正。修正后的有限元模型能较真实地反映结构的实际状态,可作为该桥梁长期健康监测与状态评估的基准有限元模型。     

Neural networks for inelastic distortional buckling capacity assessment of steel I-beams

An Artificial Neural Network (ANN) model is developed as a reliable modeling method for simulating and predicting the ultimate moment capacities for intermediate doubly-symmetric steel I-beams. The training and testing data for neural network are generated using Finite Element Analysis (FEA). In other word, an extensive numerical study was also undertaken to investigate the distortional buckling behavior of simply supported compact steel I-beams. A series of nonlinear elasto-plastic FE analyses have been carried out to simulate the distortional buckling behavior of doubly-symmetric steel I-beams, and the effects of six independent parameters as input in a lateral-distortional buckling mode has been investigated. Moreover, unlike the existing design codes the model considers the effect of web distortions in a lateral-distortional buckling mode. Then a new formula based on the ANNs has been proposed to predict the member moment capacities of steel I-beams subjected to distortional buckling. The attempt was done to evaluate a practical formula considering all parameters which may affect distortional capacity. Then, a comparison has been made between the proposed formula and the predictions from the current design rules in some structural steel codes. The results show that the proposed formula is more accurate and applicable than existing design codes. Finally, a sensitivity analysis using Garson׳s algorithm has been also developed to determine the importance of each input parameters.     

Refined 3D finite element modeling of partially-restrained connections including slip

This study presents an approach for refined parametric three-dimensional (3D) analysis of partially-restrained (PR) bolted steel beam-column connections. The models include the effects of slip by utilizing a general contact scheme. Non-linear 3D continuum elements are used for all parts of the connection and the contact conditions between all the components are explicitly recognized. A method for applying pretension in the bolts is introduced and verified. The effect of several geometrical and material parameters on the overall moment–rotation response of two connection configurations subject to static loading is studied. Models with parameters drawn from a previous experimental study of top and bottom seat angle connections are generated in order to compare the analyses with test results, with good prediction shown by the 3D refined models. The proposed 3D modeling approach is general and can be applied for accurate modeling of a wide range of other types of PR connections. A pronounced effect of slip and friction, between the connection components is shown with connections having thicker (stiffer) seat angles. This study demonstrates the effects of clamping through the bolts and contact between the components on the overall non-linear moment–rotation response. Equivalent moment–rotation responses of pull-test simulations are compared to FE model responses of full connections without web angles. The moment–rotation from the pull test is shown to be equivalent to that of the full FE model for small rotations. As the rotation increases a softer response is shown by the pull tests.     

A method for upscaling soil parameters for use in a dynamic modelling assessment of water quality in the Pyrenees

Dynamic modelling of hydrochemistry is a valuable tool to study and predict the recovery of surface waters from acidification, and to assess the effects of confounding factors (such as delayed soil response and changing climate) that cause hysteresis during reversal from acidification. The availability of soil data is often a limitation for the regional application of dynamic models. Here we present a method to upscale site-specific soil properties to a regional scale in order to circumvent that problem. The method proposed for upscaling relied on multiple regression models between soil properties and a suite of environmental variables used as predictors. Soil measurements were made during a field survey in 13 catchments in the Pyrenees (NW Spain). The environmental variables were derived from mapped or remotely sensed topographic, lithological, land-cover, and climatic information. Regression models were then used to model soil parameters, which were supplied as input for the biogeochemical model MAGIC (Model for Acidification of Groundwater In Catchments) in order to reconstruct the history of acidification in Pyrenean lakes and forecast the recovery under a scenario of reduced acid deposition. The resulting simulations were then compared with model runs using field measurements as input parameters. These comparisons showed that regional averages for the key water and soil chemistry variables were suitably reproduced when using the modelled parameters. Simulations of water chemistry at the catchment scale also showed good results, whereas simulated soil parameters reflected uncertainty in the initial modelled estimates.     

Laterally supported sandwich panels subjected to large deflections: Part 2: FE analyses and model validation

Finite element (FE) models are used for predicting the global behavior of simply supported sandwich panels fixed by bolts on the two longitudinal edges or on all their four edges. The panels are subjected to transversal distributed loads and develop large deflections. Two finite element techniques are employed: (a) utilizing effective (equivalent) continuum solid elements for the core and plate elements for the face sheets and (b) utilizing plate elements of an equivalent three-layer laminate. In the first part of this project, discussed in a companion paper, the test set-up details were presented along with the experimental results. This second part of the work presents the procedure for estimating the panel–bolt bearing stiffness, the FE analysis procedure developed to simulate the behavior of the tested panels and the validation of the numerical models. A good correlation was observed between experimental and numerical results for the displacements of the panels and the shear loads at the attachment points. The results obtained demonstrated that the proposed two-dimensional FE approach yields a good trade off between the level of accuracy and computational efficiency.     

Reliability analysis of tunnels using a metamodeling technique based on augmented radial basis functions

Metamodeling techniques have been developed and used for years in engineering reliability analysis involving expensive response simulations. In practical tunnel engineering problems where finite element (FE) simulations are required, the limited state/performance functions are in general implicit and nonlinear, and it is difficult to apply traditional gradient-based or sampling-based reliability methods, especially for large-scale problems. There is a need to develop accurate and efficient metamodels for practical tunnel engineering applications. In this paper, a metamodeling technique for reliability analysis of tunnels was studied based on augmented radial basis functions (RBFs). With a relatively small size of samples, the RBFs were used to create accurate approximate functions for different types of responses including linear and higher-order nonlinear functions. With the RBF-based metamodel constructed to express a limit state/performance function, Monte Carlo simulations (MCS) were applied to evaluate failure probability. The failure probability and reliability index obtained using the RBF-based metamodeling method were found to have good accuracy with a reasonable number of sample points. The reliability analyses of two existing tunnel examples showed that the augmented RBF metamodeling approach was efficient and effective for tunnel engineering problems.     

Seismic response of liquid-filled elevated tanks

The main focus of the current study is to evaluate the performance of elevated tanks under seismic loading. In this study, the finite element (FE) technique is used to investigate the seismic response of liquid-filled tanks. The fluid domain is modeled using displacement-based fluid elements. Both time history and modal analyses are performed on an elevated tank. Using the FE technique, impulsive and convective response components are obtained separately. Furthermore, the effect of tank wall flexibility and sloshing of the water free surface are accounted for in the FE analysis. In this study complexities associated with modeling of the conical shaped tanks are discussed. This study shows that the proposed finite element technique is capable of accounting for the fluid-structure interaction in liquid containing structures. Using this method, the study of liquid sloshing effects in tanks with complex geometries such as conical tanks is made possible. The results of this study show that the current practice predicts the response of elevated tanks with reasonable accuracy.     

饱和软土场地中地下结构非线性地震响应分析的一个FEM-IBEM耦合方法

基于Biot孔隙介质理论,提出了饱和软土场地中地下结构非线性地震响应分析的一个有限元–间接边界元(FEM-IBEM)耦合方法。方法考虑了饱和土骨架与孔隙水的动力耦合作用及饱和土–结构动力相互作用,并通过等效线性化方法考虑土体的非线性。该耦合方法的特点之一是有限元子域和间接边界元子域相互独立,非常适合并行计算,提高计算效率;特点之二是能够同时考虑有限元子域(近场)和间接边界元子域(远场)的土体非线性。通过与文献结果对比,验证了FEM–IBEM耦合方法的正确性和计算精度。以天津滨海地区一典型深厚饱和软土场地中两层双跨地铁车站为例,计算了地铁车站结构的地震内力和变形,并比较了饱和土体线性和非线性情况下地铁车站地震响应的差别,和饱和土体模型和单相土体模型情况下地铁车站地震响应的差别。研究表明:土体非线性对地铁车站结构的地震内力和变形具有显著影响;饱和土骨架和孔隙水的动力耦合作用对地铁车站结构地震内力和变形也有明显影响。     

Finite element modelling and field validation of prestressed concrete sleepers and fastening systems

Prestressed concrete sleepers and elastic fastening systems have been widely applied in North America to accommodate increased freight axle loading and the development of high-speed passenger rail systems. However, the design standard of the American Railway Engineering and Maintenance-of-Way Association remains unclear about the relationship between some critical design parameters and the vertical and lateral load paths through the track structure. In this study, field experimentation is conducted at the Transportation Technology Center in Pueblo, CO, and the test data are compared with finite element (FE) models of the track structure for model validation. Strain gauges and potentiometers are installed in the field to measure the response of concrete sleepers and fastening systems. The FE models consist of two parts: a detailed single-sleeper model to capture the local response of the loaded rail seat, and a global multi-sleeper model to provide realistic boundary conditions for the detailed model. The bond–slip behaviour between concrete and prestressing wires, and inelastic material properties are incorporated in the FE models. Good agreement is observed between the test measurement and the model output. The validated FE model is used for parametric studies on the some critical design parameters, and conclusions about the load path through the sleepers and fastening systems are summarised.     

夹层结构的声振耦合模拟及等效弹性参数计算

采用小挠度理论和有限元模型计算夹层结构的等效弹性参数。通过对比等效二维连续模型和整体三维模型,利用特征频率和特征模态分析确定连续节点如何在真空假定下受现实中不连续和夹层中填充气体或泡沫的影响。研究发现,结构单元间的离散节点会大大降低网架结构的刚度和特征频率。夹层内的气体或泡沫可增加薄板动力响应中的总体阻尼,同时必然会增大薄板的共振反应。     

考虑层间状态的沥青路面温度与荷载耦合行为分析

沥青路面是典型的层状体系,层间黏结状态的好差直接影响到路面的使用性能.采用三维非线性有限元软件ABAQUS,同时考虑沥青混合料的劲度模量随温度变化的特性,数值模拟计算了沥青路面在不同温度场状况下分别与水平及竖向荷载耦合作用的关键力学响应,分析各响应指标随层间接触状态变化的特性.研究结果表明由于接触模型作用机理的不同,其关键力学指标响应要比连续模型下的大;除路表竖向变形大小几乎与层间接触状态无关外,其他指标在低温状况下,层间接触条件变化对其影响较小,而在高温状况下,特别当层间接触摩擦系数μ＜0.6时影响很大,尤其对基层、底基层的最大拉应力及面层的最大剪应力影响显著.研究成果为科学解释沥青路面在不同环境温度与车辆荷载综合作用下的破损特征与行为机理提供了有力依据,为改善层问黏结条件有利于提高路面整体性能提供了理论支撑.     

Response of stiffened and unstiffened plates subjected to blast loading

This paper describes the results of dynamic analyses carried out on both stiffened and unstiffened panels using both simplified and advanced analytical techniques. For unstiffened panels with inplane restraint along their edges, the dynamic response of an imperfect panel was predicted using a large displacement elastic analysis based on Lagrange's equation, with the panel being treated as a shallow shell. For stiffened panels, the finite element (FE) technique was used to establish the validity of using the simplified technique to predict the inter-stiffener panel displacements for a simply supported panel. A parametric study has been carried out to analyse the effects of in-plane boundary conditions, local stiffener buckling and initial imperfections on the overall response. The significant effect of boundary conditions is demonstrated by including the actual boundary conditions of a test frame in the finite element modelling of a large-scale stiffened floorplate panel used in an experimental test series.     

Small strain based method for predicting three-dimensional soil displacements induced by braced excavation

Displacement control is a critical indicator of foundation design. Maximum deformations of soil induced by excavations are controlled by the allowable deformations of the adjacent structures. In order to evaluate potential damage of surrounding structures, Finite Element Method (FEM) is commonly adopted, predicting soil responses caused by excavations. As the numerical results obtained from FEM are greatly influenced by input material parameters of soil, inverse analysis is an effective method to obtain these parameters, which is based on the results of on-site testing. In this paper, inverse analysis based on the data of on-site testing considering Chicago clays is firstly conducted to get material parameters of soil. Then, with these input parameters, considering Hardening Soil model with Small Strain stiffness (HSS model), FEM program PLAXIS is used for parameter studies, producing coefficients in the equations of attenuation law of the displacements of the soil. Finally, considering the coupled relationship between the soil and the retaining wall, an empirical method is proposed by the authors to predict the three-dimensional displacements of soil induced by braced excavations. Validation has been done by comparisons between the results obtained by the proposed method and by other methods in the literature.     

Quasi-static response and multi-objective crashworthiness optimization of oblong tube under lateral loading

This paper addresses the energy absorption responses and crashworthiness optimization of thin-walled oblong tubes under quasi-static lateral loading. The oblong tubes were experimentally compressed using three various forms of indenters named as the flat plate, cylindrical and a point load indenter. The oblong tubes were subjected to inclined and vertical constraints to increase the energy absorption capacity of these structures. The variation in responses due to these indenters and external constraints were demonstrated. Various indicators which describe the effectiveness of energy absorbing systems were used as a marker to compare the various systems. It was found that unconstrained oblong tube (FIU) exhibited an almost ideal response when a flat plate indenter was used. The design information for such oblong tubes as energy absorbers can be generated through performing parametric study. To this end, the response surface methodology (RSM) for the design of experiments (DOE) was employed along with finite element modeling (FEM) to explore the effects of geometrical parameters on the responses of oblong tubes and to construct models for the specific energy absorption capacity (SEA) and collapse load (F) as functions of geometrical parameters. The FE model of the oblong tube was constructed and experimentally calibrated. In addition, based on the developed models of the SEA and F, multi-objective optimization design (MOD) of the oblong tube system is carried out by adopting a desirability approach to achieve maximum SEA capacity and minimum F. It is found that the optimal design of FIU can be achieved if the tube diameter and tube width are set at their minimum limits and the maximum tube thickness is chosen.     

Equivalent thickness of cold-formed thin-walled channel sections with perforated webs under compression

Cold-formed thin-walled channel sections with perforated webs (thermal studs) are widely used in external wall panels in cold regions to reduce the cold bridging effect. However, no design method appears to be available for this type of structure. A possible method is to convert the perforated web of a thermal stud into a solid one with a reduced thickness (which is referred to as the equivalent thickness) and then adopt an existing design method for solid sections (e.g. EN 1993-1-3). This paper presents the development of a method to calculate the equivalent web thickness. The equivalent thickness calculation equation is based on regression analysis of a large number of finite element simulation results of elastic local buckling strength of perforated plates under compression, considering the effects of a number of different design variables such as plate depth, thickness, perforation patterns and dimensions of the plate. The FE simulations were carried out using a general FE software. This study suggests that the equivalent thickness is mainly related to the plate width to thickness ratio, the total width of perforation at the critical section and the width of the perforation zone (total plate width between the first and last perforation). A regression equation has been proposed to relate the equivalent thickness to these parameters. To demonstrate the validity of the proposed equivalent thickness method, the compression strengths of a large range of perforated columns have been simulated by using either the original perforated sections or the equivalent solid section; and a comparison of the simulation results shows good agreement between the two sets of results.