Inverted T-beams Research Articles

Effectiveness of external prestressing in enhancing the non-ductile hanger failure mechanism in reinforced concrete inverted T-beams

Recently, inverted T-beams have been used in reinforced concrete (RC) bridges to support transverse precast stringers. Inverted T-beams, contrary to practice with conventional beams, are loaded on the flanges upper surface. This loading configuration causes hanger failure due to the generation of vertical tensile stresses near the bottom of the web. The key purpose of this study is to investigate the efficiency of vertical external prestressing stainless-steel bars in mitigating non-ductile hanger failure in reinforced concrete inverted T-beams. An experimental study on six inverted-T beams, including two un-strengthened specimens, was carried out. The study showed that the value of the prestressing level had a considerable impact on the performance of hanger mechanism in relation to crack pattern, ultimate loads, cracking behavior, load–deflection, strains, and ductility. The experimental results indicated that the suggested method for strengthening inverted T-beams had efficacy in reducing the seriousness of the non-ductile hanger failure and resulted in a strength increase of up to 53% when compared to that of the un-strengthened specimen. Additionally, two analytical models for estimating the hanger capacity and the average crack width of the strengthened RC inverted T-beams were proposed. The models that were proposed exhibited a high degree of agreement with the experimental results.

Influence of flanges geometry on the shear behavior of reinforced concrete inverted T-beams

Influence of flanges geometry on the shear behavior of reinforced concrete inverted T-beams

Effects of Web Height Reduction and Skew Angle Variation on Behavior of RC Inverted T-Beams

The use of precast inverted T-beams has been frequently used to minimize construction activities and installation time. However, shipping and placement of large invert T-beams can become challenging tasks due to their weight. Decreasing the web height of the beam can be effective in reducing the beam weight. This paper considers inverted T-beams with two overhangs, negative moment regions, and one span, a positive moment region. The examined parameters were the web height and skew angle of the inverted T-beams. To avoid high costs of testing beams and to save time, the application of numerical modeling is, hence, inevitable. A calibrated 3D nonlinear numerical model, using ATENA software, was further used to numerically investigate the effects of reducing the weight, by decreasing the web height and varying the skew angle of inverted T-beams on their structural performance. The outcomes of this study indicated that reducing the web height of the beam was an effective tool to reduce the weight without jeopardizing the strength of the beams. Increasing the skew angle of the inverted T-beam also decreased their ductility.

DESIGN OF REINFORCED CONCRETE LEDGE BEAMS - SAFETY AND ECONOMY

Safety is the key objective in structural design; however, for economy design optimization becomes an important issue. This paper looks at these two points which may seem to contradict, and tries to draw a line in order to help designers. The subject of this investigation is ledges in inverted-T beams. For safety, the strut-and-tie model as a lower bound solution contributes to the development of safe design. The nonlinear finite element as an analytical tool helps to guide designers in deciding on the optimum performance of a given design. With two tools a designer can realize where a given design stands from safety and efficiency.

Performance of Ledges in Inverted-T Beams

Performance of Ledges in Inverted-T Beams

Live-Load Distribution Factors for Composite Bridges with Precast Inverted T-Beams

Short- to medium-span composite bridges constructed with adjacent precast inverted T-beams and cast-in-place topping are intended to provide a higher degree of resistance against reflective cracking and time-dependent effects compared with voided slab and adjacent box beam systems. This paper presents the results of an analytical and experimental study performed on the first inverted T-beam bridge in Virginia. The purpose of the investigation was to quantify live-load distribution factors for shear and moment for the composite precast inverted T-beam bridge. A finite-element model of Phase I of the bridge was created and the live-load distribution factors were analytically determined. Additionally, live-load tests using a stationary truck were performed with the purpose of quantifying live-load distribution factors for moment and validating the results from the finite-element analyses. The live-load tests featured four transverse truck positions on the bridge. It is concluded that it is appropriate to estimate live-load distribution factors using provisions for cast-in-place slab-span bridges.

Inverted T-Beams: Experiments and Strut-and-Tie Modeling

Contrary to rectangular deep beams, inverted-T beams are loaded on a ledge at the bottom chord of the beam. This loading configuration induces a tension field into the web and the resulting complex strain distribution renders sectional design provisions inadequate. The applicability of strut-and-tie modeling (STM), developed for rectangular deep beams and simpler, two-dimensional designs, was evaluated. An experimental study was conducted in which 33 tests were performed on 22 large-scale reinforced concrete inverted-T beams and the effects of the following variables were investigated: ledge geometry, quantity of web reinforcement, number of point loads, member depth, and shear span-depth ratio. It was concluded that strut-and-tie modeling, although developed for much simpler structural components, offers a simple and accurate design method for the more complex strain distributions in inverted-T beams. The STM provisions developed for rectangular beams accurately captured both failure mode and ultimate capacity and are recommended for use in inverted-T beam design, as a major conclusion of this research.

Immediate Deflection of Pretensioned Inverted T-Beam with Circular Web Openings Strengthened with GFRP Using Response Surface Methodology

The urgent need for a web opening in the pretensioned inverted T-beams after the construction for essential services causes local cracking around the opening which leads to decrease in stiffness and load carrying capacity. Therefore, strengthening the vicinity of the opening is essential to restore the loss in load carrying capacity of the beam using GFRP. To study the deflection of pretentioned inverted T-beam with web opening, three-dimensional finite element beam models are developed before and after GFRP strengthening using the finite element analysis (FEA). Modeling methodology and nonlinear analysis approach in ANSYS are presented. The results obtained from the FEA beam model are compared with the test data in terms of load-deflection curve. It has been concluded that FEA models are good representations for GFRP strengthened beams with web openings in terms of the number of elements, structural details, and, especially, reasonably accurate results in general.

Ultimate load analysis of pretensioned inverted T-beams with circular web openings

The provision of transverse openings in floor beams to facilitate the passage of utility pipes and service ducts not only results in a more systematic layout of pipes and ducts, it also translates into substantial economic savings in the construction of a multi-storey building. In this paper, ultimate load analysis of statically loaded simply supported pretensioned inverted T-beams with circular web openings is presented. Major findings relevant to ultimate load analysis of pretensioned beams with circular web openings are summarized. An attempt has been made to answer the frequently asked questions related to ultimate load analysis on multiple circular web openings. It has been shown that the analysis method for pretensioned beams with multiple large circular web openings can be further simplified without sacrificing rationality.

Finite element analysis and structural design of pretensioned inverted T-beams with web openings

This paper presents the results of a research project aimed at providing standard circular web openings to the popular precast pretensioned inverted T-beam. Opening size and placement and required materials strengths were investigated. In this paper the nonlinear analysis and design of simply supported pretensioned inverted T-beam with circular web openings are presented. Two design parameters are varied: opening location and number of openings. The results from nonlinear finite element analysis were substantiated by test results from five pretensioned inverted T-beams with web opening and one solid beam. Good agreement is shown between the theoretical and the experimental results. The test results obtained from this investigation show that the performance of the specimens with web openings is almost identical to that of the specimen without web openings. A simple design method for pretensioned inverted T-beam with circular web openings is proposed.

Experimental and analytical analysis of pretensioned inverted T-beam with circular web openings

This paper presents the results of a research project aimed at providing standard circular web openings to the popular precast pretensioned inverted T-beam. The main advantage of these openings is that mechanical equipment can pass through the webs of inverted T-beams. Another advantage is a slight reduction in inverted T-beams weight that would improve the demand on the supporting frame both under gravity loading and seismic excitation. Opening size and placement and required materials strengths were investigated. Also, the effects of using straight tendons, rather than two-point depression and one-point depression, of the prestressing strands were investigated. In this paper the nonlinear analysis and design of simply supported pre-tensioned inverted T-beam with circular web openings are presented. Two design parameters are varied such as: opening location and numbers of openings. The results from a nonlinear finite element analysis are substantiated by test results from five pretensioned inverted T-beam with web opening and one solid beam. Good agreement is shown between the theoretical and the experimental results. The effect of openings on the behavior of such beams at different stages of loading is presented. The test results obtained from this investigation show that the performance of the specimens with web openings was almost identical to that of the specimen without web openings. A simple design method for estimating the cracking load for the different crack patterns is proposed. Based on these tests, design recommendations are made that will allow the addition of web openings to inverted T-beam with minimal additional calculation.

Interaction diagram and response surface plot of pretensioned inverted T-beam with circular web openings

This paper presents the results of a research project aimed at providing standard circular web openings to the popular precast pretensioned inverted T-beam. Opening diameter and placement and required materials strengths were investigated. In this paper, the non-linear analysis, interaction diagram and deflection response surface plot of simply supported pretensioned inverted T-beam with circular web openings are presented. Two design parameters are varied that is: opening location and numbers of openings. The results from non-linear finite element analysis were substantiated by test results from five pretensioned inverted T-beams with web opening and one solid beam. Good agreement is shown between the theoretical and the experimental results. The effect of openings on the behaviour of such beams at different stages of loading are presented. The test results obtained from this investigation show that the performance of the specimens with web openings was almost identical to that of the specimen without web openings. An algorithm which is written to plot interaction diagram for estimating the cracking load is proposed. Deflection response surface plots using general factorial design are also presented.

Study on Crack Resistance of Steel Fiber Reinforced Self-Stressing Concrete in Old Bridge Reinforcement

Steel Fiber Reinforced Self-stressing Concrete (SFRSSC) is a new type of fiber reinforced composite material. It has various applications in civil engineering for its well known superior properties such as self-expansive performance and high tensile resistance. However, it is not widely accepted as an effective reinforcement in the rehabilitation of the old bridges at present. The primary goal of this research is to apply SFRSSC to improve the crack resistance in the negative bending moment areas of the old bridges. Firstly, a computer analysis on the internal force of the continuous T-beams with 5 spans is given in this paper. The results show that the expansive action of SFRSSC can effectively decrease the internal force in the negative bending moment area. Meanwhile, based on the experiments of 5 composite concrete inverted T-beams, the crack resistance of the beams reinforced with SFRSSC layers is investigated. The test results obviously indicated that the composite layers enhanced the cracking moments 44.9% more than conventional concrete layers, though its height is only 13.9% of the cross section height. It is concluded that the continuous beams strengthened by SFRSSC has greatly improved the crack resistance in negative bending moment areas compared with the continuous beams strengthened by conventional concrete. According to the existing theoretical models, a procedure how to determine the self-stress is supplied and a formula which evaluating the crack resistance of composite T-beams in negative moment area is deduced in order to supply references to the old bridge rehabilitation design.

Load-Deflection Analysis of Pretensioned Inverted T-Beam with Web Openings

A precast, prestressed concrete girder with circular web openings allows building service systems (mechanical, electrical, communications, and plumbing) to cross the girder line within the member’s depth, reducing a building’s floor-to-floor height and the overall height of the structure. These height reductions have the potential to improve the competitiveness of total precast concrete structures versus other types of building systems. The experimental program reported in this paper tested five full-scale inverted-tee girders with circular web openings to failure, to evaluate the openings’ effect on girder behavior. The girders failed in a ductile manner due to diagonal cracking above the openings. The tested girders were designed using available recommendations in the existing literatures. It was observed that concrete fractured from tension zones around an opening, with cracks developing vetically towards the beam flanges. A beam would collapse when the cracks reached the flanges. In the present work, an analytical solution is developed for the load-deflection calculation of prestressed beam with web openings at any load stage. The solution assumes a trilinear deflection response characterized by the flexural cracking initiation, steel yielding, and ultimate capacity. Closed form expressions are presented for the case of simple beams subjected to four-points loading. These expressions are modified from present ACI code equations by incorporating appropriate laboratory determined coefficients in order to predict more precisely with some degree of conservativeness on flexural load-point deflection with any extent of uncracked, postcracked, and postyielded region along their spans. Accordingly, a simplified analysis procedure is developed by adopting a trilinear load-deflection response. The effectiveness of the simplified procedure is demonstrated by comparing its results to those of the analytical solution and the experimental values.

Rehabilitation of RC inverted-T girders using anchored CFRP sheets

Existing infrastructure includes significant number of reinforced concrete (RC) bridges that are old and designed based on outdated design codes. Inverted-T beams used as bentcap girders that support the bridge’s longitudinal precast beams provided a popular structural system of many existing bridges. The structural behaviour of inverted-T beam is different than that of conventional top-loaded beams, due to the fact that the loads are introduced into the bottom flange rather than the top of the beam. The objective of the present study is to experimentally examine the effectiveness of new rehabilitation techniques using anchored carbon fibre-reinforced polymer (CFRP) sheets to eliminate non-ductile failure mechanisms in hanger, web, and flange zones of RC inverted-T girders. The experimental program of this study included conducting eight tests on four simply supported RC inverted-T girders before and after rehabilitation. The girders represent a 1/3rd scale model of a prototype bentcap girder. The experimental results showed that the proposed new rehabilitation schemes proved to eliminate the non-ductile mechanisms in hanger, web, and flange zones. The rehabilitated girders were able to reach displacement ductility levels of up to 4 and showed an increase in strength up to 20% compared to the control girders.

Destructive Testing of Two Forty-Year-Old Prestressed Concrete Bridge Beams

Two specimens from a 40-year-old inverted T-beam prestressed concrete bridge were tested to destruction. These beams matched specimens tested in 1954 as the prototype for this bridge. The tests revealed that the specimens remained strong and ductile even after 40 years and that full composite action was achieved without the use of stirrups. The AASHTO Specifications provided reasonable estimates of the cracking moments and conservative estimates of the ultimate moment. The AASHTO Code also provided reasonable estimates of loss of prestress when compared to measured values. An excellent correlation was found between the specimens tested in this research and the prototype tests of 1954 in terms of load vs. deflection behavior, cracking moments and ultimate moments.

Serviceablity Behavior and Failure Mechanisms of Concrete Inverted T-Beam Bridge Bentcaps

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