Elie G. Hantouche

Stress-Strain Model for Fiber-Reinforced Polymer Jacketed Concrete Columns

Fiber-reinforced polymer (FRP) jackets are often used to confine and reinforce concrete columns. This article reports on a study of the stress-strain behavior of FRP-confined concrete columns that focused on rectangular column sections. The authors developed a new design-oriented model of the stress-strain response of FRP confined columns. Their test variables included the volumetric ratio of the FRP jackets, the aspect ratio of the column section, and the area of longitudinal and lateral steel reinforcement. Results showed that jacketing rectangular column sections with FRP sheets increases their axial strength and ductility. FRP jackets can be used to prevent premature failure of the concrete cover and buckling of the steel bars, leading to substantially improved performance. The authors include a discussion of the main parameters that control the stress and strain characteristics of FRP-confined rectangular column sections. They propose a general design model of the stress-strain response of FRP-confined concrete. The authors conclude that the results predicted by this model showed very good agreement with other test data of FRP-confined circular and rectangular columns reported in the literature.

Axial Stress-Strain Model of CFRP-Confined Concrete under Monotonic and Cyclic Loading

AbstractExperimental results of the axial stress-strain response of eighteen carbon-fiber-reinforced polymer (CFRP) confined circular, square, and rectangular column specimens when subjected to cyclic axial compression are presented and discussed. Guided by these test results and other test data reported in the technical literature, a constitutive axial stress-strain material model of CFRP-confined concrete under generalized loading is developed. The proposed model, which is composed of a monotonic envelope response and a cyclic response, accounts for a wide range of test parameters and assumes a more simplified approach than existing models available in the literature. The model covers all important parameters in a unified manner, and predicts both ascending and descending postpeak responses. In addition to its simplicity in application, despite little discrepancy, the model was able to reproduce the test results generated in the experimental part of this investigation and other test data reported in the...

Prying Models for Strength in Thick-Flange Built-Up T-Stubs with Complete Joint Penetration and Fillet Welds

AbstractThe results of a series of finite-element (FE) simulations and experimental studies are used to develop two prying models that predict the failure strength of thick-flange built-up T-stub connections with complete joint penetration (CJP) and fillet welds. A parametric study based on identifying the major geometric and force-related parameters that vary within current acceptable steel fabrication and design practices is used to select the cases for analysis. The strength prying models predict the capacity of thick-flange built-up T-stub connections with CJP and fillet welds for the failure limit state of the partial yielding tension flange followed by bolt fracture. The accuracy of the developed strength models are verified with FE results of built-up T-stubs designed for full strength compared with existing models reported in the literature. Based on the results of this study, a refined design procedure that takes into account the partial yielding in thick-flange T-stubs is proposed.

Seismic FRP Bond Strengthening of the Critical Splice Region in Wide Reinforced Concrete Columns

This paper presents preliminary results of a broader ongoing experimental study on the seismic bond strengthening of the critical reinforcement splice region in wide reinforced concrete (RC) columns or bridge piers confined with carbon fiber reinforced polymer (FRP) laminates and having bending about their minor axis. Large lateral drifts induced by strong earthquakes may result in splitting bond failure of the spliced bars, or rapid bond degradation at the splice location, leading to possible structural failure of the columns or piers. Previous research has verified the effectiveness of external confinement using FRP composites for improving bond performance of the spliced reinforcement of columns or piers having circular cross section, or rectangular cross section subjected to cyclic loading about their major axis. The preliminary experimental program reported in this paper consists of testing two full-scale wide column specimens under extreme substandard splice detailing associated with relatively short splice length, small concrete covers, small transverse spacing between the spliced bars, and complete absence of internal steel ties within the splice region. The test results showed that, despite extreme substandard splice detailing, the use of external FRP confinement improved the bond strength of the spliced bars, delayed the bond stiffness degradation under cyclic loading, and increased the energy dissipation capacity of the wide columns. However, the corresponding improvements were not as effective as anticipated. Consequently, before a final conclusion is drawn, more tests will be carried out on similar specimens but using instead more realistic and practical splice details as well as internal transverse steel ties for satisfying the minimum detailing requirements of the ACI 318-11 for gravity load designed axial members.

Isolated Shear Endplate and Double Angle Connections: Prediction of Strength Capacity

This paper presents preliminary results of an ongoing analytical study on the behavior of steel shear connections subjected to fire. Fire safety in building design has become a recent concern for researchers in the past few years. Steel beam-end connections affect significantly the overall performance of structures at elevated temperatures. Several experimental studies have been conducted on full scale beamcolumn assemblies; however, many aspects of the structural behavior and failure mechanisms that govern the behavior of steel beam-end connections at elevated temperatures are still not well characterized. The preliminary analytical program consists first of a series of finite element (FE) simulations of steel shear endplate and double angle connections that are conducted to better understand the behavior of endplate and double angle connections at elevated temperatures. Second, the FE models are validated against experimental results of shear endplate and double angle connections at ambient and elevated temperature available in the literature. A comparison is also made between the capacity predictions of the two connections at ambient and elevated temperature. The FE models are capable of predicting the behavior of double angle and shear endplate connections under varied loading conditions and elevated temperatures. The results show that rotational ductility and capacity of the double angle at ambient and elevated temperature are both larger than that of the shear endplate connection.

Mechanical modeling for predicting the axial restraint forces and rotations of steel top and seat angle connections at elevated temperatures

Purpose This paper aims at developing a mechanical-based model for predicting the thermally induced axial forces and rotation of steel top and seat angles connections with and without web angles subjected to elevated temperatures due to fire. Finite element (FE) simulations and experimental results are used to develop the mechanical model. Design/methodology/approach The model incorporates the overall connection and column-beam rotation of key component elements, and includes nonlinear behavior of bolts and base materials at elevated temperatures and some major geometric parameters that impact the behavior of such connections when exposed to fire. This includes load ratio, beam length, angle thickness, and gap distance. The mechanical model consists of multi-linear and nonlinear springs that predict each component stiffness, strength, and rotation. Findings The capability of the FE model to predict the strength of top and seat angles under fire loading was validated against full scale tests. Moreover, failure modes, temperature at failure, maximum compressive axial force, maximum rotation, and effect of web angles were all determined in the parametric study. Finally, the proposed mechanical model was validated against experimental results available in the literature and FE simulations developed as a part of this study. Originality/value The proposed model provides important insights into fire-induced axial forces and rotations and their implications on the design of steel bolted top and seat angle connections. The originality of the proposed mechanical model is that it requires low computational effort and can be used in more advanced modelling applications for fire analysis and design.

Generalized Axial Stress-Strain Response of Rectangular Columns Confined Using CFRP Jackets and Anchors

AbstractThe results of an experimental study of the cyclic axial stress-strain response of rectangular concrete columns confined with a combination carbon-fiber-reinforced polymer (CFRP) jacket and CFRP anchors are presented and discussed. The test variables include aspect ratio of the column section, area of CFRP wraps, and area and configuration of the CFRP anchors. It was found that adding CFRP anchors improves the confinement effectiveness of the CFRP jackets, leading to substantially enhanced envelope stress-strain response and ductility of axial failure. Furthermore, changing the anchor configuration while maintaining the total anchors’ cross-sectional area does not produce a noticeable effect on the envelope stress-strain curve. The cyclic part of the stress-strain response of the CFRP-anchored specimens is similar to that of the companion specimens confined with CFRP sheets without anchors. Based on the results of this study, analytical expressions are derived for predicting the stress-strain curv...

Design of Thick Plate Double-Tee Connections for Seismic Applications

AbstractDesign of thick plate double-Tee connections is discussed and evaluated based on experimental data and analytical studies. This paper summarizes the results of an extensive experimental and analytical work aiming at widening the applicability of double-Tee connections needed for deep beams that meet the performance requirements for moment-resisting frames (MRFs) in seismic areas as specified in seismic provisions. New limit states controlling the strength and deformation capacities of the connections are presented. A detailed comprehensive design methodology and design examples of thick plate double-Tee connections are developed. The proposed design procedure includes all possible yielding mechanisms and failure modes that might occur in thick plate double-Tee connections and accounts for the maximum rotational capacity demand in the connection, as required for seismic analysis and design. The information presented in this paper can be used toward prequalification of thick plate double-Tee connect...

Behavior of full strength built-up T-stub connections for seismic areas

S engineers are often involved in projects to strengthen deficient structures as a feasible alternative to cost-prohibitive full replacement of the structure. The use of composite materials to strengthen existing concrete structures by externally bonding thin laminates or strips is mature enough that design codes and guidelines are available for flexural, shear, and axial strengthening applications. Researchers have also investigated strengthening steel structures using composite material, however, the field is not as mature as it is for concrete applications. This paper presents a new strengthening technique where pultruded GFRP sections are bonded to shear deficient regions to enhance the local buckling resistance of the thin walled steel structures. The technique, referred to as strengthening-by-stiffening or SBS, was developed at Louisiana State University. An experimental program was designed to study the effect of FRP stiffener configuration on the efficiency of SBS. Different orientations, web slenderness values and aspect ratios were tested monotonically up to failure. The ultimate shear capacities beams were enhanced by a minimum of 30% when one stiffener was used on a beam with a square panel and a maximum of 56%. Post yielding behavior including the transition from a tension field to sway-frame load path will also be discussed.C walling system consisting of two skins of profiled steel sheeting and an infill of concrete is novel form of construction. Such walling system has great potential to be used as gravity and lateral load resisting elements in buildings. The strength, stiffness, ductility and energy absorbing capacity of composite walls subjected to axial, monotonic/cyclic shear and impact loadings will be described based on comprehensive experimental and theoretical investigations. The fire durability of the walls subjected to high temperatures will also be presented based on residual strength/stiffness/energy absorption capacity. The innovative feature of such walls is the use of new engineered high performance concretes (HPCs) with high strength, high ductility (strain hardening capacity) and micro-cracking characteristics developed at Ryerson University for the last few years. Such HPC composite walls have shown superior performance compared to those made with traditional concrete in terms of strength, ductility, energy absorbing capacity and durability as well as post-impact strength/stiffness/ energy absorbing capacity. Analytical models/design equations for the load resistance of composite walls are developed and their performance validated through experimental and finite element modeling.T task at the present study was the verification of the current methods used in a conventional manner so as to estimate the behavior of a tunnel against ground motion but also the investigation and suggestion of additional methods. To accomplish this objective, the study analyzes a real project that had been designed by the engineering team of Geodata. Moreover there is a review of what has already been applied to the case (pseudo-static methods) and in parallel there is a consideration of various other existent procedures: analytical, dynamic time-history and a different numerical model again in pseudo-static condition. The time-history method is highlighted in particular as it is a rigorous scheme that needs prudent consideration. In the end, the comparison brought out both advantages and drawbacks but as well as the contrasts of the distinct proceedings and made the associated proposal for future performance issues. Creating a model for a pseudo-static approach has a simplicity that makes it advisable as the primary way to characterize the situation. On the other hand, it is the only way among all those that were described at the study and can exist on its own. The model itself is capable of enclosing sufficient results provided that the configuration guarantees a reliable representation of the surrounding mass conditions (in the present case, the project adopted pure material homogeneity and a detailed grid around the tunnel). Shear deformation is the dominant value that plays the role to define the level of the response and therefore the dynamic analysis was also a tool to detect the relative strain levels. Even so, a thorough search among past ground motion scenarios brings the suitable records (the key parameter here is the PGA of the region) that can more or less set the stress-strain framework to strengthen the reliability of the numerical model. The use of time-history (dynamic) analysis requires a suitable record selection (three or more) and a number of accompanying checks. The record time-histories must be compatible to the site response spectrum and were scaled to the relevant PGA. Further checks have to do with the frequency propagation ability offered by the model but also with the energy content of the input. Even the damping issue is considered in more than one ways. Consequently, this method turns out to be a useful, representative and exceptional tool as it is the only one that inserts dynamic loading. The basic topic is the interaction and the coexistence of the dynamic analysis with any simplified numerical approach. Such a combination is to be further examined at a large group of deep elements. This study demonstrates that, the two methods, if put together, can set the analyses to the same strain levels and consequently the correlation between them will be considered much more valid so as to evaluate the seismic response of the structure.

Seismic Strengthening of Bond-Critical Regions in Wall-Type Bridge Piers Using Active Confinement

AbstractActive confinement by means of pretensioned steel anchor rods is used for bond strengthening of lap-spliced reinforcement and for improving the seismic performance of wall-type bridge piers. Representative as-built and strengthened pier specimens with lap-spliced reinforcement within the critical hinging region were tested under large drift reversals. The test parameters included ratio of pier longitudinal reinforcement, diameter of the spliced bars, and configuration of the pretensioned steel rods. The strengthened piers developed enhanced bond resistance and low bond degradation of the spliced bars, increases in the lateral load and drift capacities, and much less pinching in the lateral load–drift response when compared with the as-built specimens. In this study, a design approach is developed for engineers to evaluate the active lateral pressure required for adequate bond strengthening and for designing the strengthening system. A design example is provided to illustrate the use of the propose...