PREDICTION OF STRUCTURAL EFFECTS IN CONCRETE AFFECTED BY ALKALI-AGGREGATE REACTION

Alkali-aggregate reaction (AAR) is a chemical reaction between alkalis in concrete and certain alkali-reactive substances which are occasionally present in the aggregate. AAR produces a gel, which absorbs water, swells, inserts local stresses, and causes internal and external cracking in the concrete. Research on the reaction has been extensive. However, little research into the structural effects of AAR has been carried out and the effects are not yet adequately understood. The present research is to investigate the structural effects of AAR and to develop a numerical method for the analysis of the affected members. AAR affects the structural performance of reinforced concrete members in the following ways. • The expansion of AAR induces stresses in concrete and reinforcement and alters the bond stresses between the reinforcement and concrete. • AAR changes the material properties of the concrete. • AAR changes the bond properties between reinforcement and the concrete. To analyse an AAR affected member, the expansions within the member due to AAR have to be known. The main feature of AAR expansion is its stress dependency. This necessitates an expansion analysis to take into account the expansion and stress history of the concrete. A model for AAR expansion analysis is proposed, in which the basic variable is the free expansion and the restrained expansion of a concrete is governed by an instantaneous stress-expansion relationship. This model has been proved to yield good results. Experimental work to verify the assumptions made in the expansion model and also provide information on the deterioration of material properties of the affected concrete is described Material models are proposed based on the test results. The expansion model and the material models have been incorporated into a non-linear finite element computer program. Analytical results show good agreement with test data. The results of numerical studies carried out on singly reinforced beams conditioned with and without loading are given. The characteristics of structural performance of the beams found in the numerical studies are in general agreement with those found in laboratory and field testing. The numerical studies have helped to improve understanding of the effects of AAR on structural members. The method developed could be used to assist the future research and the appraisal of in-situ affected structures.Department of Civil and Offshore Engineering, Heriot-Watt Universit

Behaviour of R.C. beams upgraded with externally bonded steel or FRP plates

The structural behaviour of simply supported reinforced concrete (R.C.) beams strengthened in flexure by externally bonded steel or fibre reinforced plastic (FRP) plates has been investigated. A novel theoretical model coupled with simple (hence, practical) procedure(s) for designing such beams against premature plate peeling failure has been developed. The theoretical model and the design procedures have been validated by an extensive number (169) of mainly large-scale test data (using steel or FRP plates) from other sources. The effects of variations in the magnitude of Young's modulus for FRP plates on the potential changes in the flexural ultimate load of R. C. beams with externally bonded FRP plates, in the absence and/or presence of plate peeling, have been investigated in some detail with the theoretical predictions of various failure loads and associated modes of failure supported by an extensive number of test results from other sources. Moreover, brief theoretical parametric studies for other first order composite beam design parameters have also been carried out in order to clarify the effects of variations in such parameters on the predicted modes of failure. It has been shown (both, theoretically and by using large scale experimental data) that the load bearing capacity for a plated beam could (under certain circumstances) be significantly lower than even that for the corresponding unplated beam with the mode of failure being of an undesirable brittle nature. Such brittle failures can obviously have serious implications in practice, where this method has been used extensively for upgrading both bridges and buildings in a number of countries, with the design calculations very often not having properly accounted for the possible occurrence of premature plate peeling phenomenon, especially when FRP plates have been used. Further work in this area included a quantitative theoretical insight into the effect of pre-cracking of the beams (under service conditions) on the ultimate plate peeling load. A critical quantitative examination of a number of previously available theoretical models, as proposed by others, has also been carried out, and some of these models for predicting the plate peeling failure of R. C. beams have been shown to suffer from rather serious shortcomings

Nonlinear Finite Element Analysis of Reinforced Concrete Coupled Shear Walls

This thesis is concerned with the development of an inelastic material model to be used in conjunction with the finite element technique to simulate the behaviour of reinforced concrete shear-walls under lateral loads. The proposed computational model is capable of tracing the entire nonlinear response up to ultimate load conditions. The main features of the nonlinear behaviour of concrete and steel are incorporated in the numerical model. These include cracking, nonlinear biaxial stress-strain relationships in concrete up to crushing and yielding of steel. The investigation first considers the linear elastic behaviour of coupled shear-walls then a consistent material model that matches the existing experimental evidence for the behaviour of plain concrete under monotonic biaxial loading is considered. The reinforcing steel is idealized as bilinear uniaxially stressed material. The individual material models are combined with the finite element technique to demonstrate their applicability. To check the validity and accuracy of the numerical model, finite element calculations are compared with experimental results for shallow and deep beams, shear panels subjected to monotonic loading. Finally, various hypothetical coupled shear-walls and tested microconcrete shear walls were analysed highlighting the history of crack propagation, deflections, crushing of concrete and yielding of steel up to failure. The resulting model should prove to be a simple useful research tool for use in the study of any reinforced concrete structure which may be considered to be in a state of plane stress

Investigation of the Mechanical Behavior of I-Shaped Steel Beams Strengthened By Mechanically-Fastened FRP Laminates

Retrofitting and strengthening of steel structures have gained significant importance due to the highly increasing number of deteriorated steel structures in many places around the globe. The conventional method of retrofitting or strengthening of steel structures by replacing steel members or attaching additional external steel plates are usually time-consuming, corrodible, and a cumbersome task. Many of the drawbacks of the conventional retrofitting systems can be overcome through the use of Fiber Reinforced Polymers (FRP) due to their high strength-to-weight ratio. Furthermore, FRP materials are corrosion resistant, which makes them more durable especially when environmental deterioration is a concern. In recent years, the application of FRP in the strengthening of existing structures has increased considerably. A significant amount of research studies have been conducted to explore the effectiveness of implementing externally bonded FRP to strengthen reinforced concrete (RC) structures. Following the successful introduction of FRP in the strengthening of RC beams and columns, researchers started to explore the concept of using the FRP in the strengthening of steel elements. Although this idea was initially rejected by many researchers because of the significantly low elastic modulus of the FRP relative to steel, the idea started to float to the surface again when high-modulus FRP were successfully produced. The elastic modulus of such FRP approaches and even, in some cases, exceeds the elastic modulus of steel. Similar to the case of RC, researchers initially focused on the application of externally bonded FRP (EB-FRP) for flexural strengthening of steel beams. The research outcomes revealed that steel beams strengthened with EB-FRP strips exhibit unfavorable brittle failure mechanism due to debonding of the FRP. More recently, research work on application of mechanically fastened FRP (MF-FRP) to RC elements has shown promising results in term of installation efficiency, level of strengthening achieved, and, more importantly, preventing FRP delamination prior to concrete crushing. As such, a high potential exists for achieving a successful and efficient strengthening scheme when utilizing the MF-FRP laminates to strengthen steel beams. A unique study on the application of MF-FRP to steel beams was conducted by Alhadid (2011). The study revealed that MF-FRP leads to ductile response of the strengthened system provided that adequate number and strength of anchoring fasteners are used. Insufficient FRP length-to-span ratio or insufficient number of steel fasteners will result in unfavorable brittle mode of failure by shear rupture of the fasteners or tensile rupture in the FRP laminate. The driving force behind the current research study stems from the need to gain a better understanding of the mechanical behavior of the steel beams strengthened with MF-FRP laminates. The research is conducted numerically and analytically. Three-dimensional (3D) finite element (FE) analysis using the general purpose software package ANSYS is conducted in the numerical phase of the study. The 3D FE model developed in this study accounts for the effect of both material and geometrical nonlinearities in addition to the interfacial slip between the FRP laminates and the steel beam. The FE model is validated against the experimental results reported by Alhadid (2011), and excellent agreement is found. The validated FE model is then used to study the behavior of the composite steel-FRP beam parameters including the force distribution in anchoring steel fasteners, the stress distribution and spread of yielding in the steel section and the corresponding stress distribution in the FRP laminates. Furthermore, the FE model is utilized to investigate the effect of different parameters on the mechanical behavior of the strengthened beams namely: the steel section height; length, thickness and stiffness of FRP laminates; and distribution and configuration of the steel fasteners. For the analytical analysis, a closed-form analytical model is derived to predict the elastic behavior of the steel-FRP composite beams taking into consideration the slip at the steel-FRP interface. The analytical model is then utilized to evaluate the deflection, the first yielding load of the steel-FRP system and the distribution of shear forces induced in the steel fasteners. The current study concludes that the contribution of the FRP in reducing mid-span deflection and load-carrying capacity in the elastic stage (i.e., when all materials are still elastic) increases if the elastic modulus of FRP is close to or higher than the steel section. As the length of the FRP increases, the index of elastic composite action increases indicating higher efficiency of the FRP laminate, especially at low fastener stiffness. After yielding in the extreme fibers of the bottom steel flange, the FRP laminates contributes significantly in carrying the mid-span loads because the FRP laminate remain elastic and contributes significantly in carrying the tensile stresses. The study also shows that the steel beam with deeper cross-section and strengthened with MF-FRP at the bottom flange exhibits higher improvement in its flexural capacity relative to the beam with shallow section with almost the same stiffness. This is because the shear forces carried by the steel fasteners cause a bending moment in the steel beam that is proportional to the section height, and counteracts the bending moment due to the applied mid-span load. Increasing the thickness of the FRP laminate significantly improves the load-carrying capacity of composite steel-FRP beams. Provided that a sufficient number of fasteners is provided to avoid shear failure at the interface, increasing the number of steel fasteners, or reducing the pitch distance does not increase the load-carrying capacity significantly. However, it will ensure a ductile failure mode of the composite steel-FRP beams. The analytical solution used in the current study provides a convenient, but accurate, tool that can be used to calculate the deflection of the composite beam while considering interfacial slip. The solution can also be used to estimate the load that initiates yielding in the steel component of the composite beam and finding the distribution of the shear forces induced in the steel fasteners

Recent Research and Developments in Cold-formed Steel Design and Construction

Unstiffened Elements - Some Interesting Features - Tests of Profiled Steel Decks with V-Stiffeners - Bending Strength of Beams with Non-Linear Analysis - Local and Distortional Buckling of Thin-Walled Beams - Design of C-Sections Against Deformational Lip Buckling - Lateral Buckling of Singly Symmetric Beams - Flexural Capacity of Discretely Braced C\u27s and Z\u27s - The Buckling Behaviour of Hollow Flange Beams - Experimental Investigations of I-Beams - Tests of Continuous Purlins Under Downwards Loading - Tests of Full-Scale Roofing Systems - Profiled Sheet Behaviour Under Concentrated Load - On Design of Profiled Sheets with Varying Cross Sections - Properties for Cellular Decks in Negative Bending - Contrasting Behaviour of Thin Steel Roof Claddings Under Simulated Cyclonic Wind Loading - New ASCE Standards for Cold-Formed Steel Deck Slabs - Composite Slabs Analyzed by Block Bending Test - Repeated Point Loading Tests on Composite Slabs - Thermal Shielding Near Intermediate Supports of Continuous Span Composite Slabs - Design of Channels Against Distortional Buckling - Distortional Buckling of Cold-Formed Steel Z-Section Columns - Shah Alam Sports Complex: Design and Construction of Unistrut Space-Frame Roof Structure - Flexibly Connected Thin-Walled Space Frame Stability - Test of a Full Scale Roof Truss - Down-Aisle Stability of Rack Structures - Racking Performance of Plasterboard-Clad Steel Stud Walls - An Experimental Study of Shear Wall Units - Some Applications of Generalized Beam Theory - Calibration of a Bending Model for Cold-Formed Sections - Recent Development in Cold-Formed Steel - The 1989 Edition ofthe Canadian Cold-Formed Steel Design Standard - Observations and Comments Pertaining to CAN/CSA-S136-M89 - Prediction of Corner Mechanical Properties for Stainless Steels Due to Cold Forming - Stainless Steel Tubular Beams - Tests and Design - The Lateral Torsional Buckling Strength of Cold-Formed Stainless Steel Lipped Channel Beams - Testing and Design of Bolted Connections in Cold-Formed Steel Sections - Behavior of Arc Spot Weld Connections in Tension - The Bi-Axial Behaviour of Shear Connectors in Composite Slabs and Beams - Influence of Deformed Metal Decking Composite Floors to Beam-Column Connections - Education in Cold-Formed Steel Structures - Lifelong Learning - Activities of the Center for Cold-Formed Steel Structure

Finite Element Analysis of Concrete Fracture Specimens

The effects of the descending branch of the tensile stress-strain curve, fracture energy, grid refinement, and load-step size on the response of finite element models of notched concrete beams are studied. The width of the process zone and constraint of crack angles are investigated. Nonlinearity is 1 imited to cracking of the concrete. A limiting tensile stress criterion governs crack initiation. Concrete is represented as linear elastic prior to cracking. Cracks are modeled using a smeared representaion. The post-cracking behavior is controlled by the shape of the descending branch, fracture energy, crack angle, and element size. Unloading occurs at a slope equal to the i nitia 1 modulus of the material. load deflection curves and cracking patterns are used to evaluate the beam's response. Comparisons of the process zone size are made. All analyses are performed on a 200 x 200 x GOO mm concrete beam, with an initial notch length of 80 mm. The fracture energy, tensile strength, and shape of the descending branch interact to determine the stiffness and general behavior of the specimen. The width of the process zone has a negligible influence on the beam's response. The importance of proper crack orientation is demonstrated. The model is demonstrated to be objective with respect to grid refinement and load-step size

Non-linear finite element analysis of reinforced concrete panels and infilled frames under monotonic and cyclic loading. Structures under plane stress loading are analysed up to and beyond the peak load. Non-linear material properties including cracking, crushing and the non-linear behaviour at the interface of members are considered.

A non-linear finite element program to simulate the behaviour of infilled frames and plane stress reinforced concrete members under the action of monotonic and cyclic loading has been developed. Steel is modelled as a strain hardening plastic material, and in the concrete model cracking, yielding and crushing are considered. The separation, sliding, and opening and closing of initial gaps at the interfaces between the frame and the infill panels are accounted for by adjusting the properties of interface elements. The non-linear equations of equilibrium are solved using an incremental-iterative technique performed under load or displacement control. The iterative techniques use the standard and modified Newton-Raphson method or the secant Newton method. An automatic load incrementation scheme, line searches, and restart facilities are included. The capabilities of the program have been examined and demonstrated by analysing five reinforced concrete panels, a deep beam, a shear wall, and eight infilled frames. The accuracy of the analytical results was assessed by comparing them with the experimental results and those obtained analytically by other workers and shown to be good. A study of the effects of some material and numerical parameters on the results of analyses of reinforced concrete deep beam has been carried out. Two techniques have been proposed and used to overcome numerical problems associated with local strain concentrations which occur with the displacement control, when path dependent incremental iterative procedures are used for inelastic materials. The displacement control provided with these modifications has been shown to be more efficient than the load control.Iraqi Governmen