Post-installed Shear Reinforcement Research Articles

Experimental study on shear transfer across interfaces with post-installed shear reinforcement

To address the fit-up issues arising from reinforcement congestion and limited seating area over precast beams, an improved joint detail characterized by post-installed interface shear reinforcement has been developed. The incorporation of post-installed narrower looped bars as an alternative to conventional protruding stirrups significantly expedites the erection of precast flooring systems. Moreover, direct shear tests are performed on 30 Z-shaped specimens to investigate the influence of joint details, surface roughness, looped bar ratio, and embedment length of post-installed bars on the interface shear behavior. Experimental results indicate that employing post-installed narrower looped bars not only ensures adequate seating length for precast flooring systems, but also prevents the splitting failure of concrete cover which can induce the degradation of dowel action. Sufficient anchorage is the prerequisite for post-installed looped bars to impose clamping stress on concrete interface, and a shallow embedment length may trigger the occurrence of pull-out failure. Surface roughness is another factor determining the interface shear resistance and stiffness. Untreated surfaces, in contrast to intentionally roughened surfaces, are susceptible to the cohesion fracture and may hinder the development of shear-friction action. Furthermore, a linear correlation exists between looped bar ratio and the shear resistance of concrete interface. Based on the experimental results, design recommendations, including the minimum required anchorage length for post-installed looped bars, are proposed for the novel joint detail.

Experimental evaluation of flat slabs strengthened with post-installed shear bolts with pre-loading

Based on the possibility of brittle failure of flat slabs, there are relevant requirements for their strengthening in cases of deficient design or increasing loads. One of the essential factors to consider is, that an existing structure requiring strengthening always has some history of loading. An experimental study was performed in order to verify the effect of strengthening with post-installed shear reinforcement on flat slabs with pre-loading. Four full-size square flat slabs with dimensions of 2500 × 2500 mm, strengthened with shear bolts, were tested, as well as a reference slab without any shear reinforcement. The shear reinforcement was installed before loading in two specimens. For this purpose, bolts consisting of threaded rods, nuts and washers were used. Two types of threaded rods were used, i.e. rods of a diameter of 12 mm and a steel grade of 8.8 and rods of a diameter of 10 mm with 4.8 steel grade, which predestined the failure mode of the flat slab. Two other specimens were loaded up to 50% and 75% of their initial shear resistance without shear reinforcement – obtained as the resistance of the reference slab. Subsequently, they were unloaded or loaded on 50% of their resistance and strengthened with shear bolts. The pre-loading of flat slabs before strengthening demonstrated a decreasing effect on the achieved resistance of flat slabs strengthened by post-installed shear reinforcement (resistance 1715 kN for slab without pre-loading, 1647 kN for slab pre-loaded to 50% of initial resistance, and 1563 kN for slab pre-loaded to 75% of initial resistance). The measured decrease in the resistance compared to the slab strengthened before loading was 5% to 10%, depending on the pre-loading level.

Experimental Study on Reinforcement Effect of Post-Installed Shear Reinforcement on a Reinforced Concrete Column

Experimental Study on Reinforcement Effect of Post-Installed Shear Reinforcement on a Reinforced Concrete Column

ASSESSMENT ON EVALUATION OF OUT-OF-PLANE SHEAR STRENGTH OF REINFORCED CONCRETE PLATE SEISMIC-RETROFITTED WITH POST-INSTALLED SHEAR REINFORCEMENT

A post-installed shear reinforcement (PSR) method that is applied to flat plates such as foundation slabs and underground outer walls from inside the building was developed. In this study, the out-of-plane shear strength evaluation formula was proposed using the past test results. In addition, since these flat plates are subjected to seismic force while receiving earth pressure, it is expected that they will be in a complicated stress state during an earthquake. In such a case, finite element analysis is useful, so the experimental results were simulated to verify the finite element analysis method for the flat plate with PSR.

Enhanced service life of existing infrastructure buildings by use of concrete screw anchors as post-installed shear reinforcement

In the last decades, traffic on railways and roads has increased significantly in Central Europe. On the other hand, the existing infrastructure mainly origins from the late 1950s to the 1970s. This applies also for the existing bridge and tunnel infrastructure which is now up to 60 years old. Due to this age and new standards in the current codes, quite often the amount of shear reinforcement does not fulfil the current design code rules. As a replacement of existing structures is often highly unsustainable, methods to improve the shear strength are needed. Therefore, a new system for post-installed shear reinforcement by the use of concrete screws was developed at the University of Innsbruck in the last years. The idea is to use concrete screw anchors - already known as anchoring element - aspost-installed reinforcement. In over 60 shear tests with girders and slabs the excellent applicability of concrete screw anchors as post-installed shear reinforcement has been proven. Also shear tests with cyclic loading were performed prove the use for dynamically loaded structures, such as bridges. Based on these test results a design approach was determined to meet the Eurocode-2 assessment standards.Several pilot-projects with concrete screws have been realised in Austria and Germany. For example a rail-road-bridge over a German highway with a remaining service life of zero years was strengthened to a new service life of over 20 years. Also a city-centre tunnel in Munich which was erected below a historic building is currently strengthened under ongoing traffic in the tunnel using concrete screw anchors as post-installed reinforcement.

A comparison of punching shear strengthening of RC flat plates with FRP bars and steel bolts

This study investigated the behavior of carbon fiber-reinforced polymer (CFRP), aramid fiber-reinforced polymer (AFRP) bars and steel bolts as post-installed shear reinforcements for strengthening flat plate structures to evaluate their cost and performance effectiveness via a series of monotonic load tests. Seven interior slab–column connections with a square column including one control specimen and six strengthened specimens with a single-line cruciform shear reinforcement were tested. Two shear reinforcement ratio conditions were examined, which comprised four and seven bars on each side of the column corresponding to 0.75 and 0.5 times the effective slab depth, respectively. The results were compared with the well-established design guidelines, revealing that the shear capacity of the specimens with post-installed shear reinforcement increased to a level where the failure mode changed from punching shear to flexure, resulting in more ductile behavior of the specimens. Additionally, the critical shear crack theory was used to characterize the performance of the specimens; the experimental results agreed well with the theory. The study indicated that FRP materials are competitive compared to the steel material.

Evaluation of design concepts for post-installed punching shear retrofitting

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 post-installed shear reinforcement for existing flat slab systems. The estimation of the punching shear resistance depends on several variables (geometry, mechanical, material properties, etc.) with some level of uncertainty. This study aims to assess the safety and economic performance of different methods for the design of post-installed reinforcement in an existing flat slab structure endangered by punching shear, using probabilistic analysis. The methods considered include the design procedure according to the American Concrete Institute (ACI) design code, the Canadian Standards Association (CSA) design code, the European Eurocode 2 (EC2) design code and analytical method based on the Critical Shear Crack Theory (CSCT). The probabilistic analysis was conducted based on the Monte Carlo simulation technique implemented using a MATLAB code developed in this study. The reliability index obtained for EC2 design procedure was found to be close to the EN 1990 target reliability level. CSCT and CSA, on the other hand, have a low-reliability index for most of the cases investigated.

Undercut and Grouted Anchors as Post-Installed Shear Reinforcement

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address

First experiences with concrete screw anchors as postinstalled shear reinforcement in concrete bridges

AbstractDue to growing traffic volume and more restrictive design standards, structural engineers require new strengthening systems for concrete structures. Especially the level of calculated shear reinforcement has increased with the introduction of the Eurocode standards. Therefore, new methods to improve the shear strength of existing structures are needed. Concrete screws are used as a fastening system in concrete. Due to the mechanical connection, a very robust bond between the reinforcement element and the concrete is given. The new idea is to use these anchoring elements as postinstalled shear reinforcement. To show the usability and enhancements of the new method, several test series with concrete girders have been performed at the University of Innsbruck. Using concrete screws in several different configurations all test beams showed a remarkable increase in shear‐load capacity. With a new design approach derived from the test results it was possible to apply the new system to several pilot‐projects. One slab bridge built in the 1970s was strengthened to the load level according to Eurocode. Another pilot‐project was realized at a railway bridge with a two span concrete box girder. This bridge was built with tendons vulnerable to stress corrosion cracking. To ensure a ductile failure, strengthening was necessary which was realized with concrete screws under ongoing traffic on and underneath the bridge. Currently a shear strengthening of a city tunnel in the central area of Munich is planned. In the roof slab about 7000 concrete screws are projected to be installed as shear and bending strengthening system.

Flat slab strengthening techniques against punching-shear

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.

Screw Anchors Used as Post-Installed Shear Reinforcement in Flat Slabs

More restrictive requirements of new codes, increasing of imposed loads connected with usage change of the existing structures, errors in design process or during execution can lead to necessity of the strengthening of the existing buildings. In paper, the new and modern strengthening system of flat slabs against punching shear using screw anchors is presented. Screw anchors are installed from lower face of the slab into vertically drilled boreholes. After the installation, the screw anchors operate as punching shear reinforcement. The advantages of the system are significant resistance and deformation capacity increment of the flat slab as well as easy and fast installation with no need to drill through the whole slab thickness and access the upper face of the slab. System is suitable for strengthening of office buildings, since removal of the flooring is not needed or in parking garages, where the water resistance is not disturbed by the system. Moreover, paper deals with special problems that are connected with design of the presented strengthening system e.g. considering of load (deformation) level of the slab at the moment of strengthening, performance of the screw anchors in cracked and non-cracked concrete and anchorage conditions improvement of the screw anchors by application of glue or mortar into the borehole prior the screw installation.

Study on Shear Strengthening Retrofit Using Post-Installed Shear Reinforcement with Anchor Plate at One End

Study on Shear Strengthening Retrofit Using Post-Installed Shear Reinforcement with Anchor Plate at One End

Performance assessment of flat slabs strengthened with a bonded reinforced-concrete overlay

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 is also provided by the added reinforcement. Particular attention must be paid to the interface between the existing slab and the BRCO, because performance gains can only be achieved if the existing slab and the new concrete layer work monolithically. Interface performance can be improved through surface preparation and mechanical connectors; the latter is recommended to avoid premature debonding failure. This paper presents an ad hoc design approach for flat slabs strengthened with BRCO based on the critical shear crack theory, which accounts for slab rotation after strengthening. This is a fundamental parameter to assess the punching capacity of the strengthened slab. The efficiency of the proposed method is confirmed by the agreement between analytical results and experimental data collected during an experimental campaign carried out at the Universidade Nova de Lisboa.

Strengthening of Flat Slabs Against Punching Shear Using Post-Installed Shear Reinforcement

First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address