Geosynthetic Reinforced Fill Material for Tennessee Bridge Approach Slab Support

The approach slab is constructed at bridge ends to serve as a smooth transition from the highway pavement to the bridge deck. However, motorists usually complain about a sudden change in elevation (bump) at the highway/approach slab (H/S) joint that causes a potential hazard for public safety, damage to vehicles, and rider discomfort. This paper develops a finite element (FE) analysis for the differential settlement at the H/S joint when supported by a strip footing that sits on compacted layers of soil embankment with uniaxial geogrid reinforcement. A parametric study was conducted to select the optimum design that consists of five geogrid layers equally spaced within a depth of 2 [Formula: see text] below the strip footing, where [Formula: see text] is the width of the footing. The inclusion of geogrid reinforcement did not only enhance the ultimate bearing stress of the strip footing but also redistributed the vertical loads over a wider region of soil embankment and thus reduced settlement. A case study is also presented for modeling the performance of a preliminary design proposed by Tennessee Department of Transportation (TDOT) for the retrofit of bridge ends. The FE analysis showed a 30%–40% improvement in the ultimate bearing stress of the strip footing when the geogrid reinforcement proposed by TDOT is extended to a depth of 1.5 [Formula: see text] below the footing.

Numerical analyses on mechanical performance of flat buried approach slab and soil deformation

<p><br clear="none"/></p><p>The vulnerability problem of expansion joints could be fundamentally resolved using the concept of jointless bridges. The longitudinal deformation of the superstructure can be transferred to the backfill by using the approach slab. The flat buried approach slab (FBAS) has been used in many jointless bridges in European countries. In order to understand the mechanical performance of FBAS and soil deformation, a finite element model (FEM) was implemented in PLAXIS. Considering the friction between the FBAS and soil, the buried depth, the FBAS length and thickness as parameters, a parametric analysis was carried out. According to the obtained results and in order to reduce the soil deformation above the FBAS, it is suggested to increase the friction between the FBAS and sandy soil, and the buried depth of FBAS. Moreover, it should be paid attention to the vertical soil deformation and the concrete tensile stress of FBAS in pulling condition.</p>

Experimental Study on Dynamic Response Characteristics of RPC and RC Micro Piles in SAJBs

The pile foundations below approach slab in a semi-integral abutment jointless bridge (SAJB) that requires high flexibility to accommodate the horizontal cyclic deformation of approach slab generated by the girder’s thermal expansion and contraction as well as earthquake action. In this paper, reactive powder concrete (RPC) and reinforce concrete (RC) micro piles were designed and fabricated. The shaking table tests on dynamic response of micro piles-soil interaction were conducted to investigate the dynamic response characteristics such as the strain time history of pile-soil system, the bending moment, and the deformation of piles. The maximum strain response of piles was observed at the buried depth of 4.2 D (D is the diameter of pile). Meanwhile, the maximum bending moments of RPC and RC piles appear at the depth of 0.64 D and 0.42 D, respectively, under the dynamic load excitation, and the peak horizontal deformation of piles were observed at pile head. It is found that the bending moment and the strain response of the RPC pile are larger than that of the RC micro pile, and increased by 40% and 98%, respectively. The RPC micro pile has better crack resistance, higher ductility, and flexural rigidity than that of the RC pile, and it can be widely used as pile foundations in SAJBs for the earthquake area.

Research on Friction between Grade Flat Approach Slab and Sliding Material in Jointless Bridges

<p>The application of jointless bridges has been increasing year by year, because it could reduce the life‐cycle cost and improve the riding comfort. The approach slab in jointless bridges does not only have the function of road transition which is the same as the approach slab in bridges with expansion joints, but also transfer and absorb the deformation produced by the thermal expansion and contraction of the girder. The Grade Flat Approach Slab (GFAS) horizontally placed on the subgrade is one of the most common types of the approach slab in jointless bridges. The material placed between GFAS and subgrade should be able to properly slide to reduce the stress in GFAS. The friction coefficient between GFAS and sliding material is an important parameter affecting the mechanical behavior of GFAS in jointless bridges. In this paper, the tests of GFAS with different sliding materials subjected to horizontal displacement were conducted to obtain the corresponding friction coefficients (from 0.34 to 0.68). The mathematical model of bilinear spring could be adapted to simulate the friction function between GFAS and different sliding materials. One Deck‐Extension Bridge (DEB) that is one type of jointless bridges was chosen as a case study. The finite element model was implemented by using Midas‐Civil software. The influence of GFAS with different sliding materials on the mechanical properties of DEB under temperature variation was investigated. It can be concluded that the influence of the friction coefficient between GFAS and sliding material on the bending moment of DEB should be taken into account.</p>

Parametrical Study of the Shear Resistance of the Approach Slabs

The transition zone of the road bridges is located right behind the abutment. Function of this structure is to ease the vehicle transition from the bridge on the rigid support to the embankment with much smaller stiffness. The main function of the approach slab is, as a part of the transition zone, helping the backfill to overcome different stiffness of the bridge foundations and embankment. The paper deals with shear resistance of the slabs for different lengths and widths. Parametrical study was performed according to Eurocode loading model 1 (Uniformed distributed load and Tandem system). Each of the analysed slabs was loaded with sets of different TS positions and location of the loading lanes. Envelopes of the shear forces of the approach slabs were analysed for each type of the slab. After that shear resistance of the slab with or without the shear reinforcement was calculated. The slab was divided into areas with same shear reinforcement distribution. The analysis is the part of the engineering tool for the bridge designers. According to length and width of the slab, the engineer can easily choose the shear reinforcement diameter and its distribution. The tool also provides the construction details of the shear reinforcement. There will be also the option for the reinforcement design of the slab, with hints for the structural scheme and calculation method.

Investigation on the performance of bridge approach slab

In Egypt, where highway bridges are to be constructed on soft cohesive soils, the bridge abutments are usually founded on rigid piles, whereas the earth embankments for the bridge approaches are directly founded on the natural soft ground. Consequently, excessive differential settlement frequently occurs between the bridge deck and the bridge approaches resulting in a “bump” at both ends of the bridge deck. Such a bump not only creates a rough and uncomfortable ride but also represents a hazardous condition to traffic. One effective technique to cope with the bump problem is to use a reinforced concrete approach slab to provide a smooth grade transition between the bridge deck and the approach pavement. Investigating the geotechnical and structural performance of approach slabs and revealing the fundamental affecting factors have become mandatory. In this paper, a 2-D finite element model is employed to investigate the performance of approach slabs. Moreover, an extensive parametric study is carried out to appraise the relatively optimum geometries of approach slab, i.e. slab length, thickness, embedded depth and slope, that can yield permissible bumps. Different geo-mechanical conditions of the cohesive foundation soil and the fill material of the bridge embankment are examined.

Field study using additional rails and an approach slab as a transition zone from slab track to the ballasted track

An abrupt change in the stiffness of railway tracks at the junction between slab track and ballasted track causes increased dynamic loads, asymmetric settlements, damage of track components, and, consequently, increased maintenance costs. Due to this, a transition zone is usually built at the junction between the ballasted and the ballastless tracks to reduce the aforementioned problems. One of the methods suggested as a transition zone in these areas is to use a combination of an approach slab and additional rails. This study evaluates the dynamic behavior of this type of transition zone using field tests and also compares its performance with a transition zone built only with an approach slab. Hence, in the Tehran–Karaj railway line, two types of transition zones were constructed: one including only the approach slab and the other one including additional rails and an approach slab. Then, by conducting some field tests, the dynamic behavior of the track in these two types of transition zones was examined. The results of the field measurements show that for the analyzed case study, at the combined transition zone with additional rails and an approach slab, instead of a sudden increase in rail displacements from the slab track to the ballasted track (i.e. by 53%), initially, in the first part of the transition zone (with additional rails and an approach slab), the deflections increase by an average of 31%, and then in the second part of the transition zone (with additional rails only) the deflections increase additionally by 11%.