Showing papers in "Journal of Structural Engineering-asce in 2001"

Anchorage strength models for FRP and steel plates bonded to concrete

Abstract: External bonding of steel plates has been used to strengthen deficient reinforced-concrete structures since the 1960s. In recent years, fiber-reinforced polymer (FRP) plates have been increasingly used to replace steel plates due to their superior properties. A key issue in the design of an effective retrofitting solution using externally bonded plates is the end anchorage strength. This paper first presents a review of current anchorage strength models for both FRP-to-concrete and steel-to-concrete bonded joints under shear. These models are then assessed with experimental data collected from the literature, revealing the deficiencies of all existing models. Finally, a new simple and rational model is proposed based on an existing fracture mechanics analysis and experimental observations. This new model not only matches experimental observations of bond strength closely, but also correctly predicts the effective bond length. The new model is thus suitable for practical application in the design of FRP-to-concrete as well as steel-to-concrete bonded joints.

Posttensioned Seismic-Resistant Connections for Steel Frames

Abstract: Steel moment-resisting frames (MRFs) with posttensioned connections are constructed by posttensioning beams to columns using high strength strands. Top and seat angles are added to provide energy dissipation and redundancy under seismic loading. This new type of connection has several advantages, including the following: (1) field welding is not required; (2) the connection stiffness is similar to that of a welded connection; (3) the connection is self-centering; and (4) significant damage to the MRF is confined to the angles of the connection. An analytical model based on fiber elements was developed for these connections. Experimental test results were used to calibrate the model. The model was used for inelastic static analyses of interior connection subassembages as well as dynamic time history analyses of a six-story steel MRF. A self-centering capability and adequate stiffness, strength, and ductility were observed in the results of these analyses. Time history analysis results show that the seismic...

Cyclic Analysis of Wood Shear Walls

Abstract: A simple numerical model to predict the load-displacement response and energy dissipation characteristics of wood shear walls under general quasi-static cyclic loading is presented. In this model the shear wall is comprised of three structural components: rigid framing members, linear elastic sheathing panels, and nonlinear sheathing-to-framing connectors. The hysteretic model for the sheathing-to-framing connector takes account of pinching behavior and strength and stiffness degradation under cyclic loading. A robust displacement control solution strategy is utilized to predict the wall response under general cyclic loading protocols. The shear wall model has been incorporated into the computer program CASHEW (Cyclic Analysis of SHEar Walls). The predictive capabilities of this program are compared with monotonic and cyclic tests of full-scale wood shear walls. It is shown that this model can accurately predict the load-displacement response and energy dissipation characteristic of wood shear walls under general cyclic loading. As an application of the CASHEW program, a procedure is presented for calibrating a single degree-of-freedom system to predict the complete nonlinear dynamic response of shear walls under seismic loading.

Advanced Mechanics of Materials

Abstract: Thu, 06 Dec 2018 03:08:00 GMT advanced mechanics of materials i pdf 11.1 BASIC RELATIONS 391 We use cylindrical coordinates r, 9, z for radial, circumferential, and axial directions. Let the cylinder be loaded as shown in Figure 11.1. Tue, 04 Dec 2018 14:16:00 GMT Advanced Mechanics of Materials P.Berosi(6th edition).pdf Advanced Mechanics of Materials and Applied Elasticity Fifth Edition ANSEL C. UGURAL SAUL K. FENSTER Upper Saddle River, NJ • Boston • Indianapolis • San Francisco Fri, 07 Dec 2018 11:50:00 GMT Advanced Mechanics of Materials and Elasticity SIXTH EDITIONADVANCED MECHANICS OF MATERIALS ARTHUR P. BORES1 Professor Emeritus Civil and Architectural Engineering ... Fri, 07 Dec 2018 13:01:00 GMT Advanced Mechanics of Materials PDF Free Download Download advanced mechanics of materials and applied elasticity in PDF and ePub Formats for free. Also available for mobi and docx. Read advanced mechanics of ... Thu, 06 Dec 2018 08:30:00 GMT Download PDF EPUB Advanced Mechanics Of Materials And ... Previous Page 2.5DIFFERENTIAL EQUATIONSOF MOTION OF A DEFORMABLE BODY53A comparison of Eqs. 2.47 and 2.48 yields... Thu, 22 Nov 2018 14:52:00 GMT Advanced mechanics of materials PDF Free Download Course Outline 1. Preliminaries • Principles of Mechanics of Materials • Elements of Stress and Strain • Linear Elastic Materials • Failure Criteria of Materials Mon, 03 Dec 2018 19:32:00 GMT ADVANCED MECHANICS OF MATERIALS I suranaree university of technology institute of engineering school of civil engineering 410 611 advanced mechanics of materials 1st trimester /2002 Fri, 07 Dec 2018 19:56:00 GMT ADVANCED MECHANICS OF MATERIALS engfanatic.tumcivil.com This is completed downloadable Solutions Manual for Advanced Mechanics of Materials ... pdf, instant download Materials ... Solutions Manual and Test Bank for textbooks\" Sun, 02 Dec 2018 15:23:00 GMT This is completed downloadable Solutions Manual for ... The third and final text in the series, Advanced Mechanics of Materials is described on this page. A condensed version of the book can be viewed for free. Thu, 25 Oct 2018 03:29:00 GMT Advanced Mechanics of Materials | Mechanics of Materials This text covers all topics usually treated in an advanced mechanics of materials course. ... (application/pdf) ... Mechanics of Materials (Advanced) ... Thu, 29 Nov 2018 06:23:00 GMT Advanced Mechanics of Materials, 2nd Edition Pearson Expanded elementary material, including more elementary examples and problems, helps to ease the transition from elements of mechanics of materials to advanced problems. Tue, 10 May 2011 23:57:00 GMT Wiley: Advanced Mechanics of Materials, 6th Edition ... Advanced mechanics PHYS*3400 ... The central goal of Newtonian mechanics is to deter-mine this trajectory, assuming that the force F acting on the particle is known at Mon, 03 Dec 2018 10:14:00 GMT Advanced mechanics PHYS*3400 Department of Physics PDF | In the real world all the structures are subjected to various stresses and strain, The module mechanics of materials gives an idea about traditional method of ... Fri, 07 Dec 2018 00:44:00 GMT (PDF) ADVANCED MECHANICS OF MATERIALS ASSIGNMENT Advanced Mechanics of Solids, AMOS Study Materials, Engineering Class handwritten notes, exam notes, previous year questions, PDF free download Thu, 06 Dec 2018 01:07:00 GMT Advanced Mechanics of Solids AMOS Study Materials | PDF ... Selection of lecture notes ...

Localization Issues in Force-Based Frame Elements

Abstract: This paper summarizes the results of an investigation on objective modeling and prediction of deformation localization in nonlinear force-based frame elements. Emphasis is placed on the behavior of reinforced concrete structures where localization is most likely to occur. The discussion begins with a brief review of the force-based element formulation. Next, plastic hinge behavior is classified into three categories: hardening plastic hinges, perfectly plastic hinges, and softening plastic hinges. The three types of inelastic behavior pose an increasing challenge to objective postpeak modeling. The physical and numerical characteristics of localized failure are outlined. Two regularization techniques for maintaining postpeak objectivity are proposed: (1) a constant fracture energy criterion, which provides objective response on the element force-displacement level; and (2) geometric scaling, which provides objective response on the local moment-curvature level in plastic hinge regions. The discussion conc...

Minimum Building Life-Cycle Cost Design Criteria. I: Methodology

Abstract: In view of the large damage suffered in recent earthquakes and hurricanes, building design criteria are developed to protect life and reduce damage and loss to an acceptable level. The problem is minimizing the expected total life-cycle cost with respect to the design load and resistance. Load uncertainty includes occurrence time, intensity, and duration. The costs of construction, maintenance, and failure consequences, including deaths and injuries, as well as discounting cost over time, are considered. Optimal values are obtained of design variables and target reliability under single and multiple time-varying loads. Also investigated is sensitivity of the optimal design to important loading and structural parameters. The optimal design is found to depend primarily on the limit state consequences (costs), and to a lesser degree on the structural life. For multiple hazards, the optimal design is controlled by the hazard with large uncertainty and severe failure consequences. In a companion paper applicat...

Toggle-brace-damper seismic energy dissipation systems

Abstract: Energy dissipation systems are being increasingly employed in the United States to provide enhanced seismic protection for new and retrofit building and bridge construction. The hardware utilized includes yielding steel devices, friction devices, viscoelastic solid devices, and mostly, so far, fluid viscous devices. This hardware has been used in either diagonal or chevron brace configurations. This paper presents three new configurations that utilize toggle-brace mechanisms to substantially magnify the effect of damping devices so that they can be utilized effectively in applications of small structural drift. Shake table testing of a large scale steel model structure and analysis are used to demonstrate the utility of these configurations. The experimental results demonstrate substantial increases in the damping ratio despite the use of small size damping devices, and, accordingly, significant attenuation of the seismic response of the tested stiff structure is observed. Moreover, the experimental resul...

Significance of midspan debonding failure in frp-plated concrete beams

Abstract: Reinforced concrete beams enhanced in flexure with adhesively-bonded fibre reinforced polymer plates are susceptible to a brittle form of failure, defined by delamination of the cover concrete attached to the adhesive that causes the plates to debond from the beam. This paper demonstrates that, while previous research has focused almost singularly on one debond mode in which concrete delamination progresses from the ends of the plates inwards, there exists another critical debond mode that initiates near flexural cracks in the midspan region of the plated beam and propagates out to the ends of the plates. Data from large-scale experimental work are presented to show that midspan debond action is triggered by high shear stresses transmitted from the plates through the adhesive to the cover concrete. These stresses arise initially from tension stiffening in the cracked concrete and corrosion of the embedded steel. It is shown that strain gauge data are required from both the bonded and exposed surfaces of t...

Diagonal Shear Failure and Size Effect in RC Beams without Web Reinforcement

Abstract: This paper describes a formal theory, which explains the mechanism of shear failure in reinforced concrete (RC) ordinary (slender) beams without web reinforcement. The theory determines the type of splitting of concrete responsible for the diagonal shear failure of beams under concentrated loads and the location along the shear span where this splitting occurs. A simple expression is derived for the shear stress at failure as the product of the ratio of the neutral axis depth to the effective depth of beam times the splitting tensile strength of concrete. It is also shown how the nominal shear strength can be adjusted to take into account the size effect. The derived formula from this analysis is verified by comparisons to extensive sets of experimental data from the literature, which have been obtained on slender beams with various strengths of concrete (low and high), steel ratios, shear span to depth (a/d) ratios, and geometrical sizes.

Optimal Placement of Multiple Tune Mass Dampers for Seismic Structures

Abstract: Effects of a tuned mass damper on the modal responses of a six-story building structure are studied first to demonstrate the damper's ineffectiveness in seismic applications. Multistage and multimode tuned mass dampers are then introduced. Several optimal location indices are defined based on intuitive reasoning, and a sequential procedure is proposed for practical design and placement of the dampers in seismically excited building structures. The proposed procedure is applied to place the dampers on the floors of the six-story building for maximum reduction of the accelerations under a stochastic seismic load and 13 earthquake records. Numerical results show that the multiple dampers can effectively reduce the acceleration of the uncontrolled structure by 10–25% more than a single damper. Time-history analyses indicate that the multiple dampers weighing 3% of total structural weight can reduce the floor acceleration up to 40%. The multiple dampers can even suppress the peak of acceleration responses due ...

Estimation of Inelastic Deformation Demands of SDOF Systems

Abstract: Two recently proposed and closely related approximate methods to estimate the maximum lateral inelastic deformations demands of single-degree-of-freedom (SDOF) systems subjected to earthquake ground motions are investigated. In both methods, maximum inelastic displacements are estimated from maximum elastic displacements through the use of parameters that relate the response of elastic and inelastic SDOF systems. In the first method, the maximum inelastic displacement is estimated from the maximum elastic displacement through mean strength reduction factors derived from statistical studies. In the second method, the maximum inelastic displacement is estimated from the maximum elastic displacement through inelastic displacement ratios also derived from statistical studies. It is shown that the first method is actually a first-order approximation of the second method and that only in the absence of variability the two methods provide the same result. Furthermore, it is shown that the systematic error introduced by the first method leads to underestimations of maximum inelastic displacement demands. The error is evaluated and examples using results from statistical results of the seismic response of SDOF systems are presented.

Apparent Periods of a Building. II: Time-Frequency Analysis

Abstract: In this, the second of a two-part paper, the analysis of the apparent frequency of a seven-story reinforced-concrete hotel building in Van Nuys, Calif., is extended to consider its time-dependent changes, both short and long term. The instantaneous apparent frequency is measured by two methods: windowed Fourier analysis and zero-crossings analysis. The results show that it changes from earthquake to earthquake and during a particular earthquake. The results also suggest ''self healing'' believed to result from settlement of the soil with time and dynamic compaction from aftershock shaking. Implications of such high variability of the system frequency on structural health monitoring, control of response, as well as on the design codes are discussed. Nonlinear response of the foundation soil acts as a sink of the incident seismic wave energy. It is suggested that it could be exploited in future designs to serve as a powerful and inexpensive energy-dissipation mechanism. reinforced-concrete hotel in Van Nuys, Calif. (VN7SH) by Fourier analysis. We also described an approximate model in which the soil-structure interaction phenomena are viewed in the simplest possible form, via a rigid foundation model. Be- cause the Fourier transform of the response is evaluated from the entire time history of response, the results in Part I gave an insight only into the overall changes of the apparent system frequency from one earthquake to another. The trend that emerged from the results of the Fourier analysis is a reduction of the apparent system frequency with increasing levels of shaking at the site. In this part, we study the time and ampli- tude-dependent changes of by time-frequency analysis. The ˜ f description of the building, recorded strong motion data, earth- quake damage, and full-scale ambient vibration tests con- ducted following the Northridge earthquake of 1994 were pre- sented in Part I and will not be repeated here.

Apparent Periods of a Building. I: Fourier Analysis

Abstract: This and the companion paper present an analysis of the amplitude and time-dependent changes of the apparent frequency of a seven-story reinforced-concrete hotel building in Van Nuys, Calif. Data of recorded response to 12 earthquakes are used, representing very small, intermediate, and large excitations (peak ground velocity, vmax = 0.6 2 11, 23, and 57 cm/s, causing no minor and major damage). This paper presents a description of the building structure, foundation, and surrounding soil, the strong motion data used in the analysis, the soil-structure interaction model assumed, and results of Fourier analysis of the recorded response. The results show that the apparent frequency changes form one earthquake to another. The general trend is a reduction with increasing amplitudes of motion. The smallest values (measured during the damaging motions) are 0.4 and 0.5 Hz for the longitudinal and transverse directions. The largest values are 1.1 and 1.4 Hz, respec- tively, determined from response to ambient noise after the damage occurred. This implies 64% reduction of the system frequency, or a factor '3 change, from small to large response amplitudes, and is interpreted to be caused by nonlinearities in the soil.

Minimum Building Life-Cycle Cost Design Criteria. II: Applications

Abstract: The design criteria for a nine-story office building, subject to earthquakes and winds, are developed based on the method in the companion paper The seismic and wind hazards, structural response analyses, and cost estimates are based on recent literature Structural limit states in the nonlinear range and consequences are considered The optimal design is obtained by minimizing the total expected life-cycle cost using a numerical procedure A sensitivity analysis is conducted comparing the optimal design to the important but controversial parameters, such as design life, death and injury cost, structural capacity uncertainty, and discount rate The method is applied to design under earthquakes, winds, and both hazards at Los Angeles, Seattle, and Charleston, South Carolina, and compared with current design As expected, the seismic load controls the optimal design in Los Angeles The optimal design is “dominated” by seismic load in Seattle and wind load in Charleston These hazards, however, do not “cont

Prediction of ultimate shear strength of reinforced-concrete deep beams using neural networks

Abstract: This study explores the use of artificial neural networks in predicting the ultimate shear strength of reinforced-concrete deep beams. One hundred eleven experimental data collected from the literature cover the simple case of a simply supported beam with two point loads acting symmetrically with respect to the centerline of the span. The data are arranged in a format such that 10 input parameters cover the geometrical and material properties of the deep beam and the corresponding output value is the ultimate shear strength. Among the available methods in the literature, the American Concrete Institute, strut-and-tie, and Mau-Hsu methods were selected because of their accuracy and used to calculate the shear strength of each beam in the set. Later, an artificial neural network is developed using two different software programs and the ultimate shear strength of each beam is determined form these networks. It is found that the average ratio of actual and predicted shear strength was 0.99 for the neural net...

Local buckling of composite frp shapes by discrete plate analysis

Abstract: An analytical study of local buckling of discrete laminated plates or panels of fiber-reinforced plastic (FRP) structural shapes is presented. Flanges of pultruded FRP shapes are modeled as discrete panels subjected to uniform axial in-plane loads. Two cases of composite plate analyses with different boundary con- ditions and elastic restraints on the unloaded edges are presented. By solving two transcendental equations simultaneously, the critical buckling stress resultant and the critical value of the number of buckled waves over the plate aspect ratio are obtained. Using this new solution technique and regression analysis, simplified ex- pressions for predictions of plate buckling stress resultants are efficiently formulated in terms of coefficients of boundary elastic restraints. The effects of restraint at the flange-web connection are considered, and explicit expressions for the coefficients of restraint for I- and box-sections are given; it is shown that actual cases lie between simply supported and fully restrained (clamped) conditions. The theoretical predictions show good agreement with experimental data and finite-element eigenvalue analyses for local buckling of FRP columns. In a similar manner, web plate elements of FRP shapes under in-plane shear loads are modeled with and without elastic restraints provided by the flange panels. The present formulation can be applied to several cases to determine local buckling capacities of laminated plates with elastic restraints along the unloaded edges and can be further used to predict the local buckling strength of FRP shapes, such as columns and beams.

Analytical model for predicting shear strength of squat walls

Abstract: A softened strut-and-tie model for determining the shear strength of squat walls is proposed in this paper. The proposed model originates from the strut-and-tie concept and satisfies equilibrium, compatibility, and constitutive laws of cracked reinforced concrete. The shear capacities of 62 squat walls were calculated and compared with the available experimental results, and reasonable agreement was obtained. Based on the collected experimental data in this paper, the proposed physical model was used to study the effects of boundary elements, cyclic loading, and vertical loads on the wall shear strength. The softened strut-and-tie model can be further developed to improve the current shear wall design procedures by incorporating the actual shear resisting mechanisms in predicting shear strength of walls.

Stress-Strain Relations for Cracked Tensile Concrete from RC Beam Tests

Abstract: A method for determining the stress-strain relations for concrete form short-term flexural tests of reinforced concrete members is proposed. The method is based on the smeared crack approach. Average stress-strain relations for concrete in tension (including the descending branch) and in compression are computed from experimental moment-average strain and/or moment-curvature curves. Computation of stress-strain relations is performed incrementally for the extreme surface fibers, and is based on a novel idea of using the previously computed portions of the stress-strain relations at each load increment to compute the current increments of the stress-strain relations. The proposed method has been applied to some experimental data reported in the literature. Average stress-strain curves for concrete in tension, where cracking, bond, and shrinkage effects were taken into account in an integrated manner, have been computed for beams with various depths, reinforcement ratios, and rebar diameters. These and othe...

Design of Cold-Formed Channels Subjected to Web Crippling

Abstract: A series of tests on cold-formed unlipped channels with comparatively stocky webs and subjected to web crippling is presented in this paper. The web slenderness values of the channels ranged from 15.3 to 45. The tests were conducted under the four loading conditions (End-One-Flange, Interior-One-Flange, End-Two-Flange, and Interior-Two-Flange) specified in the Australian/New Zealand and American specifications for cold-formed steel structures. The test strengths are compared with the design strengths obtained using the specifications. It is demonstrated that the design strengths predicted by the specifications are generally unconservative for unlipped channels. Test strengths as low as 43% of the design strengths were obtained. Hence, new web crippling design equations for unlipped channels are proposed in this paper. The proposed design equations are derived based on a simple plastic mechanism model, and the web crippling strength is obtained by dispersing the bearing load through the web. It is shown th...

Plastic hinge analysis

Abstract: Predicting behavior of plastic hinges subjected to large inelastic deformations caused by extreme loads such as earthquakes plays an important role in assessing maximum stable deformation capacities of framed concrete structures. This paper presents an analytical procedure that can be used to predict the behavior of plastic hinges in reinforced concrete columns. Since the behavior of plastic hinges in concrete columns is a 3D problem, the plastic hinge analysis technique considers equilibrium, compatibility, and constitutive relations in 3D space. Complex behavioral phenomena such as softening of longitudinal bars due to inelastic buckling and reinforcing cage-concrete core interaction are incorporated in the analysis. To establish a constitutive relationship for reinforcing bars under axial compression an experimental study on 56 reinforcing bar specimens having unsupported length to bar diameter ratios ranging between 4 and 10 was conducted, and results are reported herein. Finally, the suggested analytical procedure is compared with conventional analysis techniques by predicting the sectional response of concrete column specimens. It is concluded that through the use of the analytical procedure presented here it was possible to obtain realistic estimations for the maximum deformation capacities of the plastic hinge regions of the specimens that were tested under constant axial loads and reversed cyclic displacement excursions. The concrete core-reinforcing cage interaction, which caused outward deflections in longitudinal bars, did not only reduce the ductility of longitudinal bars under compression but also reduced the maximum stress that the bars were able to achieve.

Base-Isolated FCC Building: Impact Response in Northridge Earthquake

Abstract: The base-isolated Fire Command and Control (FCC) building in Los Angeles experienced strong motion during the 1994 Northridge earthquake. The California Strong Motion Instrumentation Program has instrumented the building and recorded the data during the Northridge earthquake; these data are available for performance evaluation. Impact was observed in the base-isolated FCC building during the Northridge earthquake. The objective of this study is to evaluate the seismic performance of the base-isolated FCC building during the 1994 Northridge earthquake and the effect of impact. New analytical modeling techniques are developed to analyze the base-isolated FCC building with impact and are verified using system identification. The response computed, using the developed analytical modeling techniques, is verified using recorded data. The response with and without impact is presented. The effects of impact on the structural response are evaluated. The seismic performance evaluations, comparing the response of th...

Ultimate Behavior of Bolted T-Stubs I: Theoretical Model

Abstract: The work presented in this paper represents the first step of a research activity aimed at the prediction of the plastic rotation supply of partial-strength bolted connections, starting from the knowledge of their geometrical and mechanical properties, by means of the component approach. As the main sources of plastic deformation of such connections are due to the components commonly modeled by means of an equivalent T-stub, the prediction of the plastic deformation capacity of bolted T-stubs is of primary importance within the framework of the component approach. Therefore, a theoretical model for predicting the plastic deformation capacity of bolted T-stubs is presented in this paper. The collapse mechanism typologies of bolted T-stubs are analyzed, and the corresponding formulations for predicting the ultimate value of the plastic displacement are given. Although the primary aim of the model is the prediction of the plastic deformation capacity, it can also be used for an approximate evaluation of the whole force-displacement curve. To evaluate the accuracy of the proposed model, an experimental program has been carried out. The experimental results and the comparison with the theoretical predictions are presented in a companion paper, providing a satisfactory agreement between theoretical results and experimental evidence.

Applied Element Simulation of RC Structures under Cyclic Loading

Abstract: A new extension for the applied-element method for structural analysis is introduced. In this method, the structure is modeled as an assembly of elements made by dividing the structure virtually. This paper first introduces the element formulation of the applied-element method. Next, the effects of the element size and arrangement are discussed, and finally, the accuracy of the proposed method in a nonlinear material case is verified by studying the behavior of RC structures under cyclic loading. For effects caused by the size and arrangement of the elements, it is shown that accurate results of stresses and strains can be obtained if elements of small size are used. As for failure behavior simulation of RC structures, the complicated behavior of cracks in structures subjected to cyclic loading, such as crack initiation and propagation, and opening and closure of cracks during the unloading process, can be simulated automatically and without any use of complicated techniques. No special knowledge about th...

Gust Loading Factor: New Model

Abstract: Wind loads on structures under the buffeting action of wind gusts have traditionally been treated by the gust loading factor (GLF) method in most major codes and standards around the world. In this...

Stiffness Modeling of Bolted T-Stub Connection Components

Abstract: The results of 48 T-stub component tests and eight full-scale T-stub connection tests are used to develop and calibrate a comprehensive T-stub connection stiffness model. The model, based on basic component spring theory, incorporates deformations from tension bolt elongation, bending of the T-stub flange, elongation of the T-stem, slip of the T-stub relative to the beam flange, bearing deformation of the T-stem, and bearing deformation of the beam flange. Nonlinear material models, for both the tension bolts and the T-stub base material, are included. A sophisticated slip/bearing routine accounts for the misalignment of shear bolt holes and variable slip conditions. Comparisons of multilinear model predictions with experimental data show that the model accurately predicts connection stiffness response and deformation at failure.

Disturbed stress field model for reinforced concrete: implementation

Abstract: The Disturbed Stress Field Model (DSFM) is a smeared delayed-rotating-crack model, proposed recently as an alternative to fully fixed or fully rotating crack models, for representing the behavior of cracked reinforced concrete. It is an extension of the modified compression field theory; advancements relate to the inclusion of crack shear slip in the element compatibility relations, the decoupling of principal stress and principal strain directions, and a revised look at compression softening and tension stiffening mechanisms. This paper describes a procedure for implementing the formulations of the DSFM into a nonlinear finite-element algorithm. The procedure is based on a total-load secant-stiffness approach, wherein the crack slip displacements are treated as offset strains. Computational aspects of the formulation are shown to be simple and numerically robust. The hybrid crack slip formulation used is found to accurately model the divergence of stress and strain directions, providing an improved representation of behavior. Predictions of shear strength and failure mode are significantly influenced in some cases.

New Model for Shear Failure of RC Interior Beam-Column Connections

Abstract: The primary objective of this study is to point out an irrationality in the existing models for shear failure, adopted by current design codes for reinforced concrete (RC) monolithic interior beam-column connec- tions. To investigate this issue, 20 tests of RC interior beam-column connections exhibiting shear failure are reexamined. Test data indicated that joint shear stress is not proportional to story shear. Joint shear increased until the end of the test in most specimens, even if the joint shear deformation apparently increased and the story shear decreased. Moment in section at the beam end decreased due to a reduction in distance between stress resultants at the column face. The cause of the deterioration of story shear is shown to originate from a finite upper limit of anchorage capacity of beam longitudinal reinforcements passing through the beam-column connection. A new mathematical model is introduced for shear failure of the beam-column connection to reflect this behavior.

Strength and ductility of fiber-reinforced high-strength concrete columns

Abstract: High-strength concrete has been used in many lower story columns of high-rise buildings, as well as low-rise and mid-rise buildings, bridges, and foundation piles. This study tested 21 high-strength, fiber-reinforced concrete columns consisting of nine 155-mm square columns and twelve 200-mm square columns. The concrete mix contained 2% (by weight) of end-hooked steel fibers and with concrete strengths ranging from 67 MPa to 88 MPa. The columns were tested in either concentric or eccentric compression with varying initial loading eccentricities. The study showed that the introduction of steel fibers into the mix design arrested the early spalling of the cover and increased the load capacity as well as the ductility of the columns over that of comparable nonfiber-reinforced specimens.

Ultimate behavior of bolted t-stubs. ii: model validation

Abstract: This paper presents results of an experimental program devoted to the validation of a theoretical model for predicting the ultimate behavior of bolted t-stubs under monotonic loading conditions. 12 specimens were tested, under displacement control, to evaluate their plastic deformation supply. The specimens are characterized by different values of the ratio between the flexural resistance of the flanges and the axial resistance of the bolts, covering the whole range of practical design situations. The results from experimental evidence are compared with force vs. displacement curves predicted by means of the theoretical model presented in a companion paper. This comparison provides the validation of the proposed theoretical model, whose primary aim is the evaluation of the plastic deformation capacity of the most important component of bolted connections. Finally, by means of the validated theoretical model, the role of the parameters affecting the plastic deformation supply of bolted connections is stressed.