Design of Reinforced Concrete Ledge Beams - Safety and Economy (original) (raw)
Related papers
Development of Design Guidelines for Ledges of L-Shaped Beams
Pci Journal, 2018
■ A procedure to evaluate the punching shear strength of the ledge was developed to provide an improved margin of safety for ledge capacity under a wide range of loading conditions. This paper is part of a series of three that reports research on the behavior and punching shear strength of ledges of L-shaped beams. The research program included experimental tests of 21 short beams of 15.5 ft (4.72 m) span, 8 long beams of 45.5 ft (13.9 m) span, and 1 long beam of 36.5 ft (11.1 m) span. All short beams were reinforced with mild steel only, while all long beams were prestressed, except for one 45.5 ft span beam. All beams were subjected to multiple tests at different locations along the ledge, resulting in 106 total tests in the program. The results of these tests were presented in the first two papers in this series. In addition to the test program, the research also included the development of a three-dimensional nonlinear finite element model (FEM), validated by the experimental da...
Reinforced concrete L-shaped beams are frequently used in the precast concrete industry specially in bridges construction to support a series of deck beams. The spandrel acts as a hanger for the ledge part, hence hanging reinforcement is used in the spandrel for this action. It was supposed that the outer vertical stirrups' branches are the main hanging elements for the ledge part; however, adding internal vertical branches contribute in hanging the ledge part. The perception that the outer vertical stirrups' branches solely are the main hanging elements and the neglection of the effect of inner stirrups' branches in hanging action can become questionable as it leads to using a great amount of outer reinforcement which leads to nesting of this part and increasing the fabrication cost of the beam. Therefore, a need exists to evaluate the contribution of the inner stirrups with the hanging steel reinforcement. This study aims to numerically model the performance of ledge beams taking into consideration distribution and amount of inner stirrups reinforcement, eccentricity of acting load on the capacity and performance of ledge beam.
Ledge behavior and strength of long-span L-shaped beams
2018
■ The experimental results demonstrate that increasing the global stress reduces ledge capacity, while the use of prestressing increases the capacity, as does concentrating the ledge reinforcement at the load location. L-shaped ledge beams are frequently used by the precast concrete industry to support floor systems such as double-tee beams. The ledges are typically subjected to heavy concentrated loads with eccentricity and must be carefully designed to effectively transfer these loads to the web of the beam. Generally, these ledges perform satisfactorily when designed by the procedure included in the seventh edition of the PCI Design Handbook: Precast and Prestressed Concrete, referred to as the PCI procedure in this paper. However, since 1985, several engineers and researchers have expressed concerns about the procedure because research findings indicate that the PCI procedure may overestimate the punching-shear failure load of the ledge.
Verification of simplified optimum designs for reinforced concrete beams
2011
Current demand on resources have forced engineering sector to look at more efficient design and construction methods. Methods that will yield better designs that are cost effective and puts less demand on decreasing resources. In this dissertation the use of topology optimisation for the design of concrete beams is investigated. The method uses topology optimisation to obtain the optimum strut-and-tie model (STM) and then uses the STM provisions of AS3600:2009 to design the beam. As a control a similar beam is designed using the conventional design methods and both beams are tested. Test results showed that the conventional beam performed better then the optimum beam and it was concluded that construction methods utilised maybe the reason for this results. It has been recommended that further research in this area is required with better construction procedures implemented.
The strut-and-tie model and the finite element - good design companions
Journal of Structural Engineering & Applied Mechanics, 2020
The strut-and-tie method (STM) can serve as a tool for a safe design of concrete structures or members. It aids to trace the flow of forces, appropriately lay-out the reinforcement, and safely predict the structure capacity. On the other hand, the linear elastic finite element can be utilized as an alternative in the development of the strut-and-tie models besides the load path method. In addition, the nonlinear finite element analysis assists in the optimization of the design results obtained from the STM. Hence, the two methods work well as companions in structural design. In order to demonstrate such understanding, different examples which include a deep beam with large opening and recess, continuous deep beams with and without openings, and beam ledges, have been utilized. In the STM solutions, the ACI 318-14 failure criteria have been adopted. In the nonlinear finite element analysis, material nonlinearity has been accounted for. The obtained solutions from the two methods, alo...
Ledge behavior and strength of short-span L-shaped beams
2018
■ The study found that several parameters affected the ledge capacity but are not considered by the PCI procedure. Precast concrete L-shaped spandrel beams are commonly used in parking structures to support deck members such as double-tee beams. The ledge is cast at the bottom of one face of the web to transfer the eccentric loads from the stems of the double-tee beams resting on the ledge. The L-shaped spandrel beams are simply supported by column haunches or corbels and are connected laterally to the columns to prevent out-of-plane rotation. The deck members are typically connected to the inner surface of the web to limit the lateral displacements of the spandrel beam. The eccentric concentrated loads from the double-tee stems cause both vertical and lateral deflections, as well as rotations of the spandrel beam.
The strut-and-tie models in reinforced concrete structures analysed by a numerical technique
Revista IBRACON de Estruturas e Materiais, 2013
The strut-and-tie models are appropriate to design and to detail certain types of structural elements in reinforced concrete and in regions of stress concentrations, called "D" regions. This is a good model representation of the structural behavior and mechanism. The numerical techniques presented herein are used to identify stress regions which represent the strut-and-tie elements and to quantify their respective efforts. Elastic linear plane problems are analyzed using strut-and-tie models by coupling the classical evolutionary structural optimization, ESO, and a new variant called SESO - Smoothing ESO, for finite element formulation. The SESO method is based on the procedure of gradual reduction of stiffness contribution of the inefficient elements at lower stress until it no longer has any influence. Optimal topologies of strut-and-tie models are presented in several instances with good settings comparing with other pioneer works allowing the design of reinforcement fo...
Inverted T-Beams: Experiments and Strut-and-Tie Modeling
ACI Structural Journal, 2015
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.
Truss Models for Concrete Member Design (Part II)
In the previous issue of Civil Computing, we discussed the application of strut and tie models to determine the force distribution within concrete members, in general, and deep members in particular. This, the second and last part of this article, deals with the determination of the reinforcement from the analysis of strut and tie model.
DESIGN OF REINFORCED CONCRETE BEAMS WITH OPENINGS
Ordinary beams with openings and deep beams with and without openings are considered disturbed regions where their strains within any section are significantly nonlinear. Therefore, it is not adequate to design those regions using either bending theory or conventional shear design equations. Hence, it is essential to rely on a rational method such as the strut-and-tie model. The behavior of experimentally tested reinforced normal- and high- strength concrete simply supported shallow beams (with and without openings) and simple and continuous deep beams (with openings) was studied. In this study, the Strutand-Tie Models STM for all such selected beams are suggested based on the available experimental results of crack patterns, modes of failure, and internal stresses trajectors obtained from elastic finite element analysis. The obtained STM results are compared with test results. To draw a complete picture of the response of the studied beams, a 3D nonlinear finite element analysis is conducted. From which, the output results of cracking patterns, deflections, failure mode and strain and stress distributions (that can not be obtained using the strut-and-tie model) are obtained In addition, a full design procedure along with numerical examples, reinforcement detailing, and design recommendations for beams with openings only is presented.