Flange Of Girder Research Articles

The fatigue strength of misaligned butt welded joints in the steel girder flange

The fatigue strength of misaligned butt welded joints in the steel girder flange

The Analysing of Coupled Bending Tosion and Shear-Lag of Curved Box Girder Bridge Considering Prestress and Initial Curvature

Based on the theory of thin-walled curved bar and considered the impact of initial curvature and prestress on the vertical flexure, the shear lag warp displacement function is replenished on the basic deformation of the curved box girder flange plate, for which the longitudinal dispersive function is utilized. According to the energy functional differential methods, the coupled bending tosion and shear lag of elasticity governing differential equations of curved prestressed box girder are deduced with different boundary conditions in considering prestress and initial curvature. The numerical solution is gained by Galerlein method. The calculated value of this article coincides well with the value of the experiment and finite-element method. It builds the theory analysing basic of shear lag effect of curved box girder bridge considering prestress and initial curvature.

The Analysing of Coupled Bending Tosion and Shear-Lag of Curved Box Girder Bridge Considering Prestress and Initial Curvature

Based on the theory of thin-walled curved bar and considered the impact of initial curvature and prestress on the vertical flexure, the shear lag warp displacement function is replenished on the basic deformation of the curved box girder flange plate, for which the longitudinal dispersive function is utilized. According to the energy functional differential methods, the coupled bending tosion and shear lag of elasticity governing differential equations of curved prestressed box girder are deduced with different boundary conditions in considering prestress and initial curvature. The numerical solution is gained by Galerlein method. The calculated value of this article coincides well with the value of the experiment and finite-element method. It builds the theory analysing basic of shear lag effect of curved box girder bridge considering prestress and initial curvature.

Experimental evaluation of GFRP bars as reinforcement for concrete bridge decks: Negative bending low cycle fatigue study

Bridge deck durability is often compromised due to corrosion of the steel reinforcement. The use of glass fiber reinforced polymer (GFRP) bars as a substitute for steel is a possible solution to this problematic condition. GFRP is an elastic brittle material with a high tensile strength, and modulus of elasticity that is approximately 20% that of steel reinforcement. Considering these material properties, meaningful data is required to demonstrate compliance with imposed design limits at all relevant limit states. Experimental evaluation of GFRP bars as structural reinforcement for highway bridge decks must recognize and duplicate the load and support conditions specific to this application. Laboratory testing should consider load magnitudes associated with AASHTO service, strength and fatigue limit states, indeterminacy of the deck in the transverse direction, two-way distribution of wheel loads, and load application and deck support conditions as affected by truck tire contact area and girder flange stiffness, respectively. In this research study 2-span continuous concrete beams doubly reinforced with GFRP bars are tested under load and support conditions designed to simulate performance of the GFRP reinforcement in a highway bridge deck environment. Monotonic, cyclic, and low cycle fatigue loading are applied to establish behavior of the experimental deck as related to an actual bridge deck load condition. Test results related to strength, deflection, and crack width are presented.

Ultimate limit state of orthotropic steel plates of composite bridges

In traditional orthotropic plates the trapezoidal longitudinal stiffener is welded to the transverse girder web and to the bottom flange of the main girder. In a recently developed orthotropic plate the stiffeners and the transverse girder web are not connected. This approach provides for a significant reduction in the amount of flame cutting and welding, but more importantly there is no longer a need to assess the fatigue condition of the weld between the stiffener and the web. On the other hand, the potential for local buckling of the free edge of the web near the trapezoidal stiffener must be considered.

접착제를 사용한 CFRP와 강재 이음부의 강도 해석

본 연구에서는 강재가 맞대기 이음으로 연결될 경우 CFRP(Carbon Fiber Reinforced Plastic) 쉬트(sheet)를 맞대기 이음부에 접착할 경우 강재 및 CFRP 쉬트에 발생하는 응력을 해석하였다. CFRP 쉬트로 보강한 경우 접착제의 두께, 강재와의 접착 길이, CFRP 강도 변화를 매개변수로 사용하여 이 매개변수에 변화에 따른 이음부의 응력분포를 분석하였다. 또한 CFRP를 여러 층으로 접착할 경우 각 층의 강도를 다르게 변화시켜 맞대기 이음부에 유리한 응력분포를 나타내는 CFRP의 강도를 제시하였다. 본 연구를 위해 빠른 수렴성을 가지며 왜곡된 요소형상에서도 정확한 응력결과를 보이는 강화변형률장(Enhanced Assumed Strain Field)을 사용한 평면변형률 유한요소에 대한 프로그램을 작성하였다. This paper presents the stress distribution of the damaged butt joint of steel plate using CFRP laminates when the flange in tension zone of steel box girder is welded by butt welding. When CFRP sheets are patched on tension flange of steel-box girder, the stress distribution of a vertical and normal direction on damaged welding part is shown as parameters such as a variation of the thickness of adhesive, the overlap length with steel, and the modulus of elasticity of CFRP sheets. For the study, we wrote the computer program using the EAS(Enhanced assumed strain) finite element method for plane strain that has a very fast convergency and exact stress for distorted shape.

Damage Monitoring and Field Analysis of Dynamic Responses of Ha Shuang Prestressed Concrete Box Girder Oblique Bridge before Strengthening

Ha Shuang Bridge is located in Harbin city within Heilongjiang province in the east north of China. The purposes of this study are to monitor the damage in structural members of Ha Shuang prestressed concrete box girder oblique bridge before strengthening and to evaluate the dynamic performance of the bridge structure by adopting dynamic load test. Monitoring process of damage of the bridge structure shows that the web of box girder in the quarter of the second span (about 10.5m from the pier) suffers from serious shear cracks. These cracks extend from the top to lower flange of box girder. The width of cracks rang from 0.5mm to 2mm and the angle is 45 degree. There are 6 bending cracks. The spacing between these cracks rang from 20cm to 30cm and the width is 035mm. In the span No. 3 near the pier, the web of box girder appears 12 diagonal cracks have width rang from 0.1mm to 0.12 mm. The results of dynamic load test analysis show that the values of measured vertical natural frequency is w1 = 3.616Hz and horizontal natural frequency w2 = 4.492Hz less than the values of theoretical natural frequency which is 3.863Hz and 4.848Hz, indicating that the actual stiffness of the bridge structure is less than the theoretical stiffness. Therefore the dynamic working state of bridge structure is not good. Therefore the working state of bridge is not good and it need to repair and strengthening.

Precast, prestressed girder camber variability

Precast concrete girder camber can vary significantly between the time of prestress release and the time of erection. This occurs even in cases in which two identically prestressed concrete girders are stored in the same manner and erected at the same time. The variations in camber become more significant as the use of high-strength concrete, longer spans, and more heavily prestressed concrete girders continues to increase. Camber as large as 8 in. (200 mm) with 3 in. (80 mm) variability is not uncommon. This problem may not be a safety issue, but it creates challenges for designers, owners, and contractors. This paper addresses several issues related to prediction, design, and construction to accommodate variability in prestressed concrete girder camber: • In design, it is impossible to precisely predict camber. However, if modern methods for calculating modulus of elasticity, creep, and prestress loss are used, the error in estimating the mean camber should be reduced and the most probable range of camber can be predicted. • Recommendations for determining final girder seat elevations and detailing of the composite action reinforcement can be made to accommodate the predicted camber and its variability. • A frequent point of contention between the owner and the contractor is the cost incurred for concrete shims over girder flanges that are thicker than designed in order to accommodate camber that is larger than predicted. This paper includes detailed design examples. The discussion is limited to conditions up to and including application of the deck slab weight.

A Study of the Evaluation of Fatigue Crack at Welded Joint for Steel Plate Girder

Fatigue phenomenon is one of the main factors controlling the life of the steel bridges. And it is caused from accumulation of live load stress for long time under a normal condition rather than an extreme condition. In the steel plate girder railway bridge, a bending deformation is occurred on the effect of eccentric at the upper flange of inner girder. Because of the deformation, the occurrence of fatigue crack has been reported between upper flange and vertical stiffener. In this paper, visual inspection, load test and the structural analysis have been performed to find out causes of cracks of the steel plate girder railway bridge having 65-year serviced history. Also, appropriate retrofitting methods for the fatigue cracks at welded joint are suggested.

Strengthening multiple span simply-supported girder bridges using post-tensioned negative moment connection technique

A post-tensioned negative moment connection technique is proposed to strengthen old multiple span simply-supported T-section reinforced concrete (RC) girders. In this technique, old concrete is removed from girder ends and flanges, a diaphragm is placed between the two adjacent girder ends over the interior support and negative moment steel strands are installed in new cast-in-place concrete and post-tensioned to make continuity. A total of six two-span simply-supported T-section RC girders were cast and five of them strengthened using the provision of the proposed post-tensioned negative moment connections. Both laboratory tests and nonlinear finite element (FE) analysis were conducted to investigate the structural performance of the strengthened RC girders. The moment redistribution in the strengthened continuous RC girders was also measured and is discussed. It is shown that the proposed post-tensioned moment connection technique can reliably transfer the negative moment over the support and markedly increase member stiffness and the load-carrying capacity of existing multiple span simply-supported RC girders. The validity of the FE analysis was also demonstrated through comparisons with experimental results.

Numerical Analysis of the Effect of Cope Hole on the Fatigue Strength of Corrugated Web Girders

A common means of facilitating cross welding on the girder flange is to use cope hole on the girder web. This paper presents a study on the fatigue strength of the corrugated web girders with the cope hole using numerical analysis. Typical stress concentration behaviours are discussed relative to reported experimental results, and parameter variations are then used to study the stress gradient on the corrugated web as the influence of the cope hole. Based on the simplified cumulative fatigue summation implemented in fatigue post-processor, fatigue life predictions are presented with codified curves of AASHTO LRFD.

Out-Plane Distortion Induced Fatigue Analysis of Steel Bridges

Induced forces in secondary steel bridge members such as diaphragms and cross-bracing can cause out-of-plane distortion in webs that may lead to fatigue cracking. Such cracking is most likely to occur if the distortion must be accommodated in a short length of the web, such as in the gap between the end of transverse stiffeners and girder flanges, because the web gap is subject to double curvature. In this paper, the numerical analysis model of a real 3-span continue steel bridge was established using ANSYS software to calculate the real fatigue stress at the web gaps. Some key structural parameters, for example, web gap depth and web thickness, have been considered in the numerical models. The results show that web thickness and web gap depth give the great affection on the out-of-plane distortion fatigue stress at web gaps.

Long-term effect analysis of prestressed concrete box-girder bridge widening

To make an analysis of long-term effect of prestressed concrete box-girder bridge widening, a revised method of shrinkage and creep is presented by incremental method on base of energy principle. Continuous change of stress aroused by concrete shrinkage and Young’s modulus of concrete over each time interval is considered, and creep effect due to constrained shrinkage strain is also taken into account. A calculating program was compiled according to this method, which was validated by test results. Then an example of prestressed concrete box-girder bridge widening was analyzed by use of this program. According to calculated results, longitudinal tensile stress at the flange of the new girder can reach 2.84 MPa due to shrinkage and creep effects of new box girder after 10 years, which may lead to crack of concrete. It is suggested that bridge widening should be performed 6 months after new girder is cast. Compared with new box girder not widened which is in service independently, the total prestressing loss of the widened new box girder decreases 31–35% 10 years after bridge widening. However, prestressing loss of the old box girder aroused by shrinkage and creep of the new box girder can be neglected.

Cracking Mechanism and Simplified Design Method for Bottom Flange in Prestressed Concrete Box Girder Bridge

Serious cracking has occurred frequently in the bottom flange of box girders during construction in recent years. This paper aims at studying the cracking mechanism and countermeasures. The stress field in the bottom flange associated with the bottom continuity tendon is presented, and the propagation of cracks during tensioning is simulated by nonlinear analysis according to the actual construction sequence. A cracking mode, which is not easy to detect in field investigation, is illustrated through numerical and theoretical study. It is caused by the deficient shear strength of the bottom flange attributed to the void in tendon ducts. Based on numerical results and field investigation, four types of cracking in the bottom flange are proposed and discussed, and a simplified design method is recommended for control of cracking.

Obtaining optimal performance with reinforcement-free concrete highway bridge decks

This article describes an application of nonlinear finite element modeling (FEM) and analysis in the selection of design details to provide desirable performance in reinforcement-free concrete highway bridge decks. The FEM approach was used to predict the ultimate capacity and failure modes of decks considered as constrained membranes. Lateral constraint of the deck (membrane) provides extra wheel load capacity for reinforcement-free bridge decks on bulb tee wide flanged concrete girders. The wide flange precast prestressed concrete girder sections currently used in bridges result in a shorter effective span for the bridge deck between the wide girder top flanges. The failure mode of concrete decks on these girders with wheel loading is expected to be punching shear. The shear forces from the vehicle wheel loads in the reinforcement-free bridge deck are designed to be carried by compressive membrane action without using reinforcing in the concrete. The compressive membrane action is enhanced by the natural lateral stiffness of the wide girder flanges and by tying adjacent girders together with steel rods placed between the webs. An experimental study of a restrained deck element was performed to identify the failure mode and to use as a basis for verifying the nonlinear properties used in finite element analysis. A parametric study using nonlinear finite element analysis was performed to investigate the factors affecting the ultimate capacity and the failure modes of reinforcement-free bridge decks on wide flange precast girders and to provide a basis for selecting desirable design details.

Steel Girder Stability during Bridge Erection: AASHTO LRFD Check on L/b Ratios

The erection of steel plate girders during the construction process of a steel bridge is a complex operation, which is often left to the contractor and/or the subcontractor to plan and execute. Rules of thumb have been developed through experience to check the lateral torsional buckling of the steel girder during erection using the maximum L/b (unbraced length/compressive flange width) ratio, below which no lateral torsional buckling would occur. Although the L/b ratio check has proven to be useful and convenient on-site, it is necessary to provide a more rational basis for the rules of thumb, and find the maximum L/b ratios by checking the lateral torsional buckling failure of girders under erection according to the latest AASHTO LRFD code. A series of parametric studies were conducted on cantilever and simply supported girders under self-weight as well as self-weight plus wind load, in order to: (1) check the rules of thumb on L/b ratios and (2) determine the effects of girder flange width, flange thick...

Effects of overheight truck impacts on intermediate diaphragms in prestressed concrete bridge girders

This paper studies the capacity of prestressed concrete bridge girders to withstand overheight truck impacts. The numerical model of the bridge was validated with the existing experimental data in the literature. The elastic-plastic modeling of concrete damage and quasi-static impact simulation of the bridge were considered. Parametric studies were then conducted with respect to the spacing and depth of intermediate diaphragms as well as girder types from which the role of intermediate diaphragms in protection and enhancement of prestressed concrete bridge girders from truck impacts is obtained. From the simulation results, it was concluded that the optimum spacing of intermediate diaphragms (that is, 25.0 ft [7.62 m]) is consistent with the results reported for previous studies. The depth of intermediate diaphragms should be extended to the top edge of the bottom flange of girders to provide maximum impact protection. Wide flanges in girders increase the bending stiffness and reduce the horizontal deflection and correspondingly decrease damage areas. However, deep webs in girders introduce a large rotation with respect to the deck, and thus increase the deflection under the truck impact. Design guidelines for typical parameters for intermediate diaphragms in prestressed concrete bridges are provided. The numerical finite-element parametric study provides a better understanding of placement and size of intermediate diaphragms in prestressed concrete bridges and their role in protecting girders from overheight truck impacts.

Stiffness requirement for flat-bar longitudinal stiffener of box-girder compression flanges

In this paper, the moment of inertia requirement of flat-bar longitudinal stiffener of bottom flange in steel box girder is investigated through finite element modeling. The required minimum stiffness for longitudinal stiffeners of box girder flange is given in the AASHTO LRFD Bridge Design Specification and is modified by Yoo. However, this requirement is adopted for T-shape stiffeners. Here, the effect of important parameters on the minimum required moment of inertia of flat-bar stiffener is numerically investigated by examining the anti-symmetric mode of buckling. This study presents the results that are based on 3D finite-element analysis of four hundred hypothetical compression flange models stiffened by varying numbers of flat-bar longitudinal stiffeners with realistic dimensions such as the height of stiffener, the thickness of the compression flange, the number of longitudinal stiffeners and the aspect ratio of plate panel. A new proposed equation for required minimum stiffness of the flat-bar longitudinal stiffeners is derived from nonlinear regression analyses. Beside that the study has taken into account the effect of boundary conditions and the effect of inelastic transition on the critical buckling stress of compression flange. Through the evaluation of a design example, the validity and reliability of the new proposed equation is demonstrated.

Shear Diaphragm Bracing of Beams. II: Design Requirements

Light gauge metal decking is commonly used in the building and bridge industries for concrete formwork. In addition to supporting the wet concrete, the metal forms also improve the lateral-torsional buckling capacity of the beams or girders they are fastened to since they behave as a shear diaphragm and restrain the warping deformation of the top flange. The design requirements for shear diaphragm bracing are not well established. This is the second part of a two-part paper. The first part of the paper focused on the general stability bracing behavior for shear diaphragms connected to the top flanges of adjacent beams or girders. This part of the paper outlines the design requirements for shear diaphragm bracing and focuses on both the stiffness and strength requirements for beam stability. Design expressions are presented for the stiffness and strength requirements as well as a model that can be used to estimate the forces in the fasteners that connect the diaphragms to the top flanges of the beams. An example is presented at the end of the paper demonstrating the use of the design expressions.

Shear Diaphragm Bracing of Beams. I: Stiffness and Strength Behavior

Light gauge metal decking is commonly used in the building and bridge industries for concrete formwork. In addition to supporting the concrete, the metal forms also improve the lateral-torsional buckling capacity of the beam or girder they are fastened to as they behave as a shear diaphragm and restrain the warping deformation of the top flange. However, the stability bracing requirements for shear diaphragms are not well established. This is the first part of a two-part paper on diaphragm bracing of beams. The first part of the paper focuses on behavior whereas the second part focuses on general design requirements. The diaphragms in the study were connected along two edges to the top flanges of adjacent girders. The parameters that were investigated include the diaphragm stiffness, load type, and load position. The type of loading has a significant effect on the stability bracing behavior of the shear diaphragm. Other factors that have an effect on the bracing behavior include the web slenderness and the presence of intermediate discrete braces. The results presented in the first part of the paper create the foundation for a diaphragm bracing design methodology that is developed and presented in the second part of the paper.