Abstract Over the years, the flat slab system has become a popular form of construction in many countries, particularly for multi-storey buildings such as offices or carparks. Nowadays, a considerable number of flat slab buildings requires strengthening against punching. Reasons are several, like design or construction errors, poor quality materials, not complying with new codes provisions, or increase of vertical load. This paper discusses different techniques for strengthening of R/C slabs against punching: insertion of post-installed shear reinforcement, application of external fibre reinforced polymers or a bonded reinforced concrete overlay (BRCO) on the slab top surface, enlargement of the support, application of a post-tensioning system. The authors propose a unified approach, based on the Critical Shear Crack Theory (CSCT), to evaluate the effectiveness of each strengthening technique. The attempt is to give a reading key capable of adapting to different strengthening techniques and providing a comprehensive view of the problem. The study shows that the CSCT could be easily adapted to all strengthening techniques and punching strength predictions are in good agreement with literature experimental results. This work also proposes to give designers the tool to choose which strengthening technique suits better to the specific case.
This paper deals with the experimental and theoretical evaluation of punching shear capacity of steel fiber reinforced concrete (SFRC) slab–column connections. Five experimental specimens with a thickness of 160 mm, different fiber volume contents (0, 1.0, and 1.5%) and different flexural reinforcement ratios (0.75 and 1.5%) have been tested. The experimental results were evaluated using a physical–mechanical model based on the critical shear crack theory (CSCT). The model has given a good appro...
Exponentially increasing loads, aging of bridges and new design and construction specifications request the strengthening of numerous bridges and concrete structures throughout Europe. Based on a continuous development and optimization for strengthening applications today a variety of post-tensioning systems are available in order to compensate the specific local and global lack of former design methods and to improve the existing infrastructure for years to come. Summarizing the different exter...
Punching strengthening of reinforced-concrete slabs using a bonded reinforced-concrete overlay (BRCO) is an efficient alternative to traditional strengthening systems such as post-installed shear reinforcement, enlargement of the support column, or bonded fibre-reinforced polymer strips. The BRCO technique allows for both the flexural stiffness and shear strength of existing slabs to be increased. Shear strength increases due to the greater slab thickness, while an increase in flexural stiffness...
Abstract Strengthening of concrete structures with a new concrete layer has been commonly used for columns, beams and slabs. This technique is economic and efficient for structural strengthening since it uses the same base materials, steel and concrete. It is usually applied on the compressed face of the concrete element due to concrete’s recognized behaviour under compression, posing several challenges to control cracking and resistance when applied on the tensile face. For assessing the perfor...
Last. Paolo Spinelli(UniFI: University of Florence)H-Index: 14
view all 4 authors...
In the last years the knowledge of the punching failure in R/C slabs increased thanks to several scientific studies. The progress obtained in this field is considerable, nevertheless achieved results are only taken into consideration by few Codes. The most updated code is the Model Code 2010, which adopted the Critical Shear Crack Theory (CSCT) for the punching shear capacity of R/C slab-column connections. At the same time, the EC2 formulation for punching is under revision, but the new formula...
Abstract The efficiency of the proposed strengthening method using externally applied post-tension rods in reinforced concrete external beam-column joints, which do not comply with any code requirements, is investigated. Five full-scale specimens were tested in the laboratory. They have specific deficiencies resulting from the lack of shear reinforcement in the joint and poor material properties including low strength concrete and the presence of plain round reinforcement bars. While all specime...
Abstract Sometimes, due to design mistakes or a change in the construction function results in heavier or additional loads, a flat slab may be failed by punching shear which is considered as a brittle failure. A lot of research work has been carried with the objectives of strengthening existing flat slabs against punching shear. Nevertheless, very few experimental tests have been conducted for the investigation of the behavior of repaired flat slabs damaged due to punching shear. An experimental...
Abstract In this paper, a system for repairing damaged flat plates as a result of punching shear is presented. The system depends mainly on repairing the damaged concrete and the addition of vertical studs with different arrangements through holes drilled in the plates. The experimental program consists of eight specimens with the same dimensions and flexural reinforcements, but with different concrete strength and shear reinforcement ratios. The main aim of the tests is to assess the efficiency...
#2Ratchanon Dithaem(King Mongkut's University of Technology Thonburi)
Last. Qudeer Hussain(Chula: Chulalongkorn University)H-Index: 8
view all 7 authors...
The results of an experimental program on shear-strengthening of flat slabs using Glass Fiber Reinforced Polymer (GFRP) rods are presented. A total of seven specimens were tested under an upward concentric monotonic loading until failure. One specimen served as a control and was tested without any modification. The remaining six specimens were strengthened with post-installed GFRP rods in single (SG), double (DB), and radial (RD) patterns within shear critical parameters around the centric colum...
#1Luis Mercedes(UPC: Polytechnic University of Catalonia)H-Index: 3
#2Ernest Bernat-Maso(UPC: Polytechnic University of Catalonia)H-Index: 8
Last. Lluís Gil(UPC: Polytechnic University of Catalonia)H-Index: 19
view all 3 authors...
Abstract Fabric-reinforced cementitious matrix (FCRMs) are composites that produce lighter and more durable strengthening solutions. In this study, carbon and basalt fabrics were used to manufactured FRCM plate specimens. These plates were subjected to a centered punctual load with different punch diameters. Flexural failure mode was observed. Experimental tests showed that carbon and basalt fabrics improved notably the load capacity and the stiffness of mortar plates compared to unreinforced on...
Abstract This paper investigates the strengthening techniques of lightweight concrete (LWC) flat slabs vulnerable to punching shear failure. Thirteen reinforced LWC flat slab specimens were experimentally tested. The main investigated parameters were the type of shear reinforcement (steel bars, high strength bolts, or glass fiber reinforced polymers (GFRP) rods), spacing, shear reinforcement configuration around the column and the fixation method of shear reinforcement. The test results showed t...
Abstract Punching shear is a brittle and sudden mode of failure observed in reinforced concrete slabs structures. This type of failure typically occurs around the slab-column connections, due to transverse forces being highly concentrated in these areas, thereby causing the column to punch through the slab. Several methods have been proposed for retrofitting and strengthening existing flat slabs against punching shear failure using different reinforcement-types. One of these methods relies on po...
Abstract The paper is focused on the calibration of non-linear 3D finite element (FE) analyses to simulate punching failure of R/C flat slabs. The calibration procedure is developed with reference to the code ABAQUS, which is one of the most used computer codes in nonlinear modelling of R/C structures. Generally, the calibration of a nonlinear FE model is grounded on one test only, so its reliability could be limited. Here a hybrid method for the calibration of FE models of R/C flat slabs failin...
Abstract The present study investigates the strengthening of flat slabs with Externally Bonded Reinforcement “ On Grooves ” (EBROG) and “ In Grooves ” (EBRIG) FRP strips and they are compared with Externally Bonded Reinforcement (EBR) FRP strengthening. 28 slabs consisting of one control and 27 strengthened were defined and analyzed nonlinearly. The EBRIG and EBROG strengthening layout consisted of 1- or 2-layer FRP strips under slabs on 2 grooves of 4- or 8-mm width and 8, 10 or 12 mm depth. Fi...
