Mitigation of seasonal temperature change-induced problems with integral bridge abutments using EPS foam and geogrid

Expansion of bridge girders in summer moves integral bridge abutments toward backfill, causing high lateral earth pressures behind the abutment. Some backfill material slumps downward and toward the abutment when the abutment moves away from the backfill due to bridge girder contraction in winter. Placement of geogrids within the backfill can increase stability of the backfill while placement of compressible inclusions (e.g., Expanded Polystyrene (EPS) foam) can reduce lateral earth pressures behind the abutment caused by bridge girder expansion. In this study, six physical model tests were conducted with 30 abutment top movement cycles due to simulated seasonal temperature changes to study the performance of integral bridge abutments with different mitigation measures. The test results showed that geogrid reinforcements caused higher maximum lateral earth pressures at the same abutment movement, but geogrids with wrap-around facing significantly reduced the backfill surface settlements. The combination of the EPS foam and geogrids could minimize lateral earth pressure increase and backfill settlement. The EPS foam reduced the abutment toe outward movement when the abutment top was pushed against the backfill; however, the mitigation effects by the EPS foam was limited due to its small thickness and relatively high elastic modulus in this study.     

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments with different facing conditions

This paper presents an experimental study on reduced-scale model tests of geosynthetic reinforced soil (GRS) bridge abutments with modular block facing, full-height panel facing, and geosynthetic wrapped facing to investigate the influence of facing conditions on the load bearing behavior. The GRS abutment models were constructed using sand backfill and geogrid reinforcement. Test results indicate that footing settlements and facing displacements under the same applied vertical stress generally increase from full-height panel facing abutment, to modular block facing abutment, to geosynthetic wrapped facing abutment. Measured incremental vertical and lateral soil stresses for the two GRS abutments with flexible facing are generally similar, while the GRS abutment with rigid facing has larger stresses. For the GRS abutments with flexible facing, maximum reinforcement tensile strain in each layer typically occurs under the footing for the upper reinforcement layers and near the facing connections for the lower layers. For the full-height panel facing abutment, maximum reinforcement tensile strains generally occur near the facing connections.     

采用不同下部结构形式的整体式无缝桥受力特征

建立考虑桥台 土、桩-土相互作用的整体式无缝桥有限元分析模型,并选取下部结构形式、温度作用、台后填土性质以及桥梁跨径为研究参数,对比分析了采用不同下部结构形式的整体式无缝桥受力特征。结果表明:下部结构刚度越大,其对上部结构的约束作用越强,桥梁纵向整体性更明显,但对主梁梁端和桥台的受力越不利;当下部结构刚度较大时,温度对桥梁内力和变形的影响更明显;随着桥梁跨径的增大,整体温度作用的影响逐渐成为温度作用中的主要因素;当下部结构采用矮桥台与桩基础时,台后填土密实度对梁端和桥台弯矩以及主梁轴力的影响不明显;当采用墙式桥台时,随着台后填土密实度的增大,温度作用下主梁轴力会快速增大;随着桥梁跨径的增大,整体式无缝桥的内力不断增大,且当采用刚度较大的下部结构时增大的速率更快;若以桥台在正常使用极限状态下的混凝土裂缝宽度为控制目标,应对整体式无缝桥的最大桥长进行限制,且下部结构刚度越大,最大桥长的限制越严格。     

Numerical study of geosynthetic reinforced soil bridge abutment performance under static and seismic loading considering effects of bridge deck

Although the use of Geosynthetic Reinforced Soil (GRS) bridge abutments has been increasing, the seismic performance of such structures has remained a significant concern due to their unknown behavior in load-bearing and stress distribution under bridge load and seismic conditions simultaneously. This paper investigates the static and dynamic response of GRS bridge abutment. A series of numerical models representing the realistic field conditions of these structures, including two reinforced soil walls and a single span deck that restrains the top of walls, rather than equivalent surcharge load, was developed. The calibrated numerical model in FLAC program was used to evaluate the effects of horizontal restraint from the deck on the GRS wall displacements and reinforcement loads at the end of construction and under harmonic base acceleration up to 0.5 g. Results indicated that the restraint mobilized from the bridge deck presence, considerably affected the results at both the end of construction and after the dynamic load was applied. Moreover, a series of the parametric studies were performed to investigate the influences of backfill soil relative compaction, reinforcement stiffness, reinforcement length, and reinforcement vertical spacing on the response of GRS abutments at the end of construction and post dynamic state.     

Lateral earth pressure behind an integral abutment

Integral abutment bridges have gained increasing attention in the past few decades. They provide a cost-effective solution to the high maintenance expenses associated with the joints and bearings found in conventional bridges. This paper describes the observed behaviour of granular soil backfill retained behind an integral abutment subjected to cyclic loading. Significant pressure build-up was observed in the soil behind the abutment in most locations. The pressure build-up is attributed to several mechanisms such as sand particle flow and densification due to cyclic loading, and the shearing of dense sand during bridge expansion. Therefore, the applicability of using a linear soil pressure distribution assumed by the classical theories in designing the integral abutment system is discussed. Furthermore, the vertical and lateral distribution of the soil pressure behind the abutment has also been analysed. Results from the data measured show that bridge skew resulted in bigger soil pressures at the obtuse side of the abutment compared to the acute. The conclusions of this paper highlight several new design aspects, which are usually overlooked by the common design methodologies of integral abutments, that more accurately predict the vertical and lateral variation in the soil pressure behind abutments.     

Experimental study on the load bearing behavior of geosynthetic reinforced soil bridge abutments on yielding foundation

This paper presents an experimental study of the load bearing behavior of geosynthetic reinforced soil (GRS) bridge abutments constructed on yielding clay foundation. The effects of two different ground improvement methods for the yielding clay foundation, including reinforced soil foundation and stone column foundation, were evaluated. The clay foundation was prepared using kaolin and consolidated to reach desired shear strength. The 1/5-scale GRS abutment models with a height of 0.8 m were constructed using sand backfill, geogrid reinforcement, and modular block facing. For the GRS abutments on three different yielding foundations, the reinforced soil zone had relatively uniform settlement and behaved like a composite due to the higher stiffness than the foundation layers. The wall facing moved outward with significant movements near the bottom of facing, and the foundation soil in front of facing showed obvious uplifting movements. The vertical stresses transferred from the footing load within the GRS abutment and on the foundation soil are higher for stiffer foundation. The improvement of foundation soil using geosynthetic reinforced soil and stone columns could reduce the deformations of GRS abutments on yielding foundation. Results from this study provide insights on the practical applications of GRS abutments on yielding foundation.     

连续梁桥减、隔震体系的优化设计

本文根据连续梁桥减、隔震体系设计的特点,建立了桥梁减、隔震体系优化设计公式,实现了应用结构最优化设计理论设计桥梁减、隔震支座动力控制参数,使得桥梁墩、台所受到的地震水平力最小的同时满足小震作用下桥梁结构保持弹性;强震作用下减、隔震支座发生弹塑性变形耗散地震能量的减、隔震设计思想.通过编制的桥梁减、隔震体系优化设计程序,对连续梁桥减、隔震体系优化设计进行了算例分析,得出了一些有用的结论.     

Performance of a Preloaded-Prestressed Geogrid-Reinforced Soil Pier for a Railway Bridge

A new construction method, called “the preloaded and prestressed reinforced soil method”, proposed in this paper, aims at making reinforced backfill structures very stiff and stable. To make the deformation of a reinforced backfill nearly elastic, sufficiently large preload is first applied by introducing tension into metallic tie rods that penetrate the reinforced backfill and are connected to top and bottom reaction blocks. High tensile force in the tie rods functions as prestress, increasing the confining pressure in the backfill and thus keeping the stiffness and shear strength of the backfill soil sufficiently high. In 1996, in northern Kyushu, Japan, a prototype pier of preloaded and prestressed geogrid reinforced backfill was constructed for the first time to support a pair of simple beam girders for a temporary railway bridge. An abutment of geogrid-reinforced soil retaining wall, which was neither preloaded nor prestressed, was also constructed for the same bridge by otherwise the same construction method. The behaviours of the pier and the abutment were measured during the construction and the service period of about four and a half years and subsequently full-scale loading tests were performed. It is shown that the geogrid-reinforced backfill pier became substantially stiffer against static and dynamic load by having been preloaded and being prestressed when compared to the geogrid- reinforced backfill abutment.     

Parametric and pushover analyses on integral abutment bridge

Integral abutment bridges (IABs) are jointless bridges where the girder or the deck is continuous and monolithically connected to the abutments. A usual and important problem in the design of IABs is how to deal with the soil-structure interaction behind the abutments and next to the foundation piles: this can be considered as a fundamental aspect to reach a thorough understanding of this type of structure, which requires iterative and nonlinear analysis. In this paper, a 2D simplified finite-element model of a real 400-metre-long IAB, built in the Province of Verona-Italy, is implemented and used to perform non-linear analyses on the bridge, the structural response of which is then examined in detail. A parametric study based on the variation of the soil properties behind the back-walls and around the piles is then performed. Furthermore, a temperature pushover analysis (non linear static analysis for positive and negative temperature variations) is carried out to assess the failure pattern of the bridge caused by a temperature change, considered as one of the key parameters in IAB design. Lastly, the effect of abutment stiffness is also discussed.     

Live load distribution equations for integral bridge substructures

In this study, live load distribution equations (LLDEs) for integral bridge (IB) substructures are developed. For this purpose, numerous 3-D and corresponding 2-D structural models of typical IBs are built and analyzed under AASHTO live load. In the analyses, the effect of various superstructure and substructure properties such as span length, girder spacing, girder stiffness, abutment height, pile size, pile spacing and foundation soil stiffness are considered. The results from the 2-D and 3-D analyses are then used to calculate the live load distribution factors (LLDFs) for the abutments and piles of IBs as a function of the above mentioned properties. LLDEs are then developed to estimate the live load moments and shear in the abutments and piles of IBs using these LLDFs and nonlinear regression analysis methods. It is observed that the developed LLDEs yield a reasonably good estimate of live load moment and shear in the abutments and piles of IBs.     

Numerical study on maximum reinforcement tensile forces in geosynthetic reinforced soil bridge abutments

This paper presents a numerical study of maximum reinforcement tensile forces for geosynthetic reinforced soil (GRS) bridge abutments. The backfill soil was characterized using a nonlinear elasto-plastic constitutive model that incorporates a hyperbolic stress-strain relationship with strain softening behavior and the Mohr-Coulomb failure criterion. The geogrid reinforcement was characterized using a hyperbolic load-strain-time constitutive model. The GRS bridge abutments were numerically constructed in stages, including soil compaction effects, and then loaded in stages to the service load condition (i.e., applied vertical stress?=?200?kPa) and finally to the failure condition (i.e., vertical strain?=?5%). A parametric study was conducted to investigate the effects of geogrid reinforcement, backfill soil, and abutment geometry on reinforcement tensile forces at the service load condition and failure condition. Results indicate that reinforcement vertical spacing and backfill soil friction angle have the most significant effects on magnitudes of maximum tensile forces at the service load condition. The locus of maximum tensile forces at the failure condition was found to be Y-shaped. Geogrid reinforcement parameters have little effect on the Y-shaped locus of the maximum tensile forces when no secondary reinforcement layers are included, backfill soil shear strength parameters have moderate effects, and abutment geometry parameters have significant effects.     

Parametric Analysis on an IAB Superstructure

Integral abutment bridges(IABs) are jointless bridges where the girder or the deck is continuous and connected monolithically to the abutments.A usual and important problem in the design of IABs is how to deal with the soil-structure interaction behind the abutments and next to the foundation piles: this can be considered as a fundamental aspect for the thorough understanding of this type of structures,which requires iterative and nonlinear analysis.In this paper,a 2D simplified finite-element model of a re...     

Besonderheiten bei Entwurf und Bemessung integraler Betonbrücken

Design Details of Integral Bridges An increasing number of integral bridges without expansion joints and bridge bearings have recently been constructed. Cyclic thermal displacements at the end of the structures impose strain on backfill and the foundations of the abutments. The interaction among structure, backfill and foundation must be considered during analysis and design.     

Seismic vulnerability assessment of wall pier supported highway bridges using nonlinear pushover analyses

Pushover analyses were conducted to assess the seismic vulnerability of wall pier supported highway bridges on southern Illinois priority emergency routes. Three-dimensional finite element models were developed to reflect typical hammerhead and regular wall pier bridges from a random sample of the bridge inventory. The models incorporated expected nonlinear structural and material behavior of all the bridge components—superstructure, expansion joints, approach embankments and/or abutments, bearings, wall piers, footings and/or pile caps, and pile and/or mat foundations (plus soil effects)—as well as defining failure measures for each component. Both transverse and longitudinal pushover analyses were conducted on ninety wall pier bridge models reflecting the sample population variation in bridge characteristics such as wall pier type, number of piers, skew, type of foundation, concrete reinforcement ratio, bearing type, and wall height. It was found that the population of wall pier bridges studied was generally vulnerable to wall bearing and abutment bearing failures, wall pier ductility failures, and footing shear and/or bending failures, with bridge skew leading to a coupling of the failure mechanisms from the two pushover directions.     

无伸缩缝桥梁动力特性与抗震性能研究

以福建某简支梁桥为研究背景(该桥在实际工程中已被改造为半刚性整体桥),采用MIDAS/Civil软件将原简支梁桥改造为整体桥、半整体桥与延伸桥面板桥,分别建立了5座桥的全桥有限元模型,分析了它们在地震荷载下的受力差异。结果表明:简支梁桥在地震荷载作用下易引起主梁在桥台处的落梁现象,而无缝桥可有效防止该现象的发生,其中的整体桥表现出更优的抗震性能,更适用于强震区; 在地震荷载作用下,无缝桥与简支梁桥的桩基有效作用长度均在0～10D(D为桩径)埋深范围; 整体桥桩基在大震作用下的受力性能较好,可更好地保护桩基不被破坏; 延伸桥面板桥与传统简支梁桥台底桩身受力相近,其设计可参考现行有缝桥设计规范; 无缝桥与传统简支梁桥的墩底弯矩均最大,在该处易形成塑性铰; 纵桥向地震荷载作用下,简支梁桥与延伸桥面板桥的主梁受力最不利位置分别出现在跨中与墩顶处,而整体桥、半刚性整体桥与半整体桥出现在台顶处,其受力不利部位在设计中应引起重视; 该研究结果可为无缝桥的设计计算与相关规范的制定提供参考。     

Seismic performance of a whole Geosynthetic Reinforced Soil – Integrated Bridge System (GRS-IBS) in shaking table test

A scaled plane-strain shaking table test was conducted in this study to investigate the seismic performance of a Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) with a full-length bridge beam resting on two GRS abutments at opposite ends subjected to earthquake motions in the longitudinal direction. This study examined the effects of different combinations of reinforcement stiffness J and spacing S_v on the seismic performance of the GRS-IBS. Test results show that reducing the reinforcement spacing was more beneficial to minimize the seismic effect on the GRS abutment as compared to increasing the reinforcement stiffness. The seismic inertial forces acted on the top of two side GRS abutments interacted with each other through the bridge beam, which led to close peak acceleration amplitudes at the locations near the bridge beam. Overall, the GRS-IBS did not experience obvious structure failure and significant displacements during and after shaking. Shaking in the longitudinal direction of the bridge beam increased the vertical stress in the reinforced soil zone. The maximum tensile forces in the upper and lower geogrid layers due to shaking happened under the center of the beam seat and at the abutment facing respectively.     

Numerical parametric study of geosynthetic reinforced soil integrated bridge system (GRS-IBS)

A 2-D finite flement model was developed in this study to conduct a FE parametric study on the effects of some variables in the performance of geosynthetic reinforced soil integrated bridge system (GRS-IBS). The variables investigated in this study include the effect of internal friction angle of backfill material, width of reinforced soil foundation (RSF), secondary reinforcement within bearing bed, setback distance, bearing width and length of reinforcement. Other important parameters such as reinforcement stiffness and spacing were previously investgated by the authors. The performance of GRS-IBS were investgated in terms of lateral facing displacement, strain distribution along reinforcement, and location of potential failure zone. The results showed that the internal friction angle of backfill material has a significant impact on the performance of GRS-IBS. The secondary reinforcement, setback distance, and bearing width have low impact on the performance of GRS-IBS. However, it was found that the width of RSF and length of reinforcement have negligible effect on the performance of GRS-IBS. Finally, the potential failure envelope of the GRS-IBS abutment was found to be a combination of punching shear failure envelope (top) that starts under the inner edge of strip footing and extends vertically downward to intersect with Rankine active failure envelope (bottom).     

浅论桥涵台背回填工程质量控制

总结了多年来桥涵台背回填工程回填处理的方法及经验,从回填材料、压实标准、施工工艺等方面进行探讨,论述了保证桥涵台背回填质量控制方法及施工措施,并提出了较合理的施工工程管理手段。     

考虑台后不平衡土压力下整体桥H型钢桩基-土相互作用内力计算方法

在台后填土作用下整体式桥台-H型钢桩-土相互作用和大不平衡土压力下(台后土表面均布荷载增大了3.81 kPa)整体式桥台-H型钢桩-土相互作用拟静力试验研究的基础上,提出了考虑台后不平衡土压力下整体桥桩基-土相互作用的内力计算方法,计算了整体桥台底弯矩和剪力以及桩身弯矩和剪力,并与现有的台后土压力理论和桥梁规范的计算值进行比较。结果表明:正向加载时,采用现有的台后土压力理论和桥梁规范计算得到的台底弯矩和剪力以及桩身弯矩和剪力均与试验结果存在较大偏差; 采用黄-林法可较准确地计算AHP模型的台底弯矩和剪力以及桩身弯矩和剪力; 对于LAHP模型,试验值均与各理论计算值相差较大; 正向加载时,随着位移荷载的增加,AHP和LAHP模型的台底和桩身弯矩均逐渐增大; 台后堆载(大不平衡土压力)对整体桥台底剪力和弯矩以及桩身的剪力和弯矩产生较大的影响,LAHP模型的台底和桩身弯矩整体上均大于AHP模型的,而LAHP模型的台底剪力小于AHP模型的,桩身剪力大于AHP模型的。     

Stochastic collocation-based nonlinear analysis of concrete bridges with uncertain parameters

This paper focuses on the stochastic response of concrete bridges considering uncertainty in bearing and abutment stiffness. A multi-span simply supported bridge with concrete girders is selected. A 3D-dimensional model is prepared, and nonlinear response history analyses are performed. For the numerical dynamic simulation, the non-sampling stochastic method based on generalized polynomial chaos (gPC) expansion is utilised. The uncertain parameters include the vertical and shear stiffness of bearings and the lateral stiffness of abutments are presented by the truncated gPC expansions. Furthermore, the system response such as base shear, acceleration, velocity and displacement in different columns is presented by gPC expansion with unknown deterministic coefficients. The stochastic Galerkin projection is employed to calculate a set of deterministic equations. A non-intrusive solution, as a set of collocation points, determines the unknown gPC coefficients of the system response and the results are compared with Monte Carlo simulations. The key advantage of spectral discretization is the combination of the mentioned method with the spatial discretization, e.g. finite element model. This study also emphasises the accuracy in results and time efficiency of the proposed non-sampling method for uncertainty quantification of stochastic systems comparing to sampling procedure (e.g. Monte Carlo simulation).