Ledge behavior and strength of long-span L-shaped beams (original) (raw)
Related papers
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.
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.
Design of Reinforced Concrete Ledge Beams - Safety and Economy
2020
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 strutand-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.
Developing a method of strengthening concrete structures: Precast Prestressed Concrete Braces
2nd National Conference on Civil Engineering, Architecture and Urban Planning of Islamic Countries, Tabriz University, 2019, 2019
There are multiple methods for seismically retrofitting existing concrete structures, such as adding jackets, adding concrete shear walls, or using FRP, CFRP, HFRP sheets; applying steel braces and external Frames or even applying external precast concrete. Another method is RC INFILLING, external post-tensioned cables, et al. A new method for strengthening concrete structure is Precast Pre-stressed concrete braces (PPCB), which were introduced by Watanabe. This method applies an X-shape concrete brace to the existing RC frame; this brace is consist of four legs and a middle section. Watanabe successfully applied this method in the lab on a half-scale of a fourstory frame. In our research, we provided a 3D-model in ABAQUS-FEA in order to Finite Element Analysis of the PPCB. The results of the numerical analysis were in compliance with the experimental work of Watanabe. Then we modified different properties to the concrete brace in order to study its behavior. Results indicated that since the compression strength of the brace was more than two times of the existing frame, it could significantly be effective in reducing lateral displacement. In the following, we have introduced two new assemblies for concrete braces: single diagonal and V-shape braces. In The single diagonal brace, the middle section is omitted, and the brace would be installed in two consecutive frames. Results of the Finite Elements Analysis indicated that this new assembly is effective. Also, we have proposed another assembly for the PPCB, V-shape, which could be more buckle resistance because it has less length, but it adds extra force to beam in the existing frame.
Lateral stability analysis of long precast prestressed concrete beams
2015
Most structures are designed according to several factors but cost and utility are usually the two main factors which are considered. Structures are normally designed for a certain period of time and must meet specific safety standards during all their design life. Furthermore, due to economic reasons, optimizing the design is essential to reduce costs and produce highly competitive products. Sometimes, engineering solutions can seem permanent but as time goes by, these solutions develop thanks to technological advances and innovative engineering approaches. Precast prestressed concrete girders are an example of this development. Since the construction of the world's first prestressed concrete bridge in Oued Al Fodda, Algeria, during the years 1936-1937, the utilization and variety of precast prestressed concrete girders in structures have steadily increase. Specially during the last two decades, an increased demand has been placed on the engineering community to extend the span ranges of precast prestressed girders. Increases in concrete strength, strand diameter and improved manufacturing processes have enabled lengthening of girders achieving lower construction time and cost savings.
Prestressed Concrete Structures
Two-way Slabs (Part 1) Welcome back to the prestressed concrete structures. This is the third lecture of module nine on special topics. In this lecture, we shall study two-way slabs.
Design And Tests Of Prestressed Concrete Beams
Fire Safety Science
A prestressed TT beam had been designed considering the ultimate limit state of bending, and considering a temperature distribution given by a graph which was valid for a section with a similar shape. When tested in a furnace, it proved to have a fire resistance of only 79 minutes instead of the 2 hours foreseen by the calculation. An investigation was made, with the help of numerical modelling, to explain the reasons of the failure and to design a new specimen. Some modifications were introduced to increase the resistance to bending forces, to shear forces and to the slip of the tendons. A modified specimen behaved satisfactory in a second test. The formula proposed in Eurocode 2 for the shear resistance of reinforced concrete elements at ambiant temperature has been adapted for the elevated temperature situation and its application allowed to accurately predict the failure mode observed in the fiist test. FIGURE 1 : half section in the elements. 24,OO 4
Lateral Stability and Concrete Strength Requirements for Precast, Prestressed Concrete Components
Pci Journal, 2020
The allowable level of temporary concrete compressive stress in precast, prestressed concrete components has been a source of debate in t e co cr te industry for many years. Traditionally, hese str sses have been considered to originate ly from the effects f prestress combined with he self-w ight of a plumb component, evaluated about the major axis. The maximum compressive stress divided by the coefficient of the compressive stress limit det rmines th r quired concrete strength. Although these emporary stresses can occur at any time f om fabrication through erect on into the structure, the critical case is usually at transfer of prestress and subsequent lifting from the form. At this stage, the prestress force is higher and the concrete strength is lower than at any other point in the life of the component. At this early age, concrete is also more susceptible to damage from high compressive stress. As materials and fabrication capabilities in the precast, prestressed concrete indust...