Dissertations / Theses on the topic 'Shear lag effect'

AN ABSTRACT OF THE THESIS OF Saurav Shrestha, for the Masters of Science degree in CIVIL ENGINEERING, presented on November 22, 2016, at Southern Illinois University Carbondale. TITLE: VERIFICATION OF SHEAR LAG IN LONGITUDINALLY WELDED TENSION MEMBERS. MAJOR PROFESSOR: Dr. J. Kent Hsiao, Ph.D., P.E. (CA), S.E. (UT) Tension members are used broadly as bracing members in buildings and truss. When double channels or double tees are welded to a gusset plate, stresses are distributed non-uniformly in connected members since only a part of its cross-section is connected. Shear lag factor describes this phenomenon. The main objective of this study is to verify shear lag factor of tension steel members with welded connections using the finite element computer analysis and the current design Specification for Structural Steel Buildings (AISC 2010). The provision for calculating shear lag factor, U, is given by AISC Specification as 1-x ̅/L for angles, tees, channels and wide flange tension members. Weld size and length of the weld are the main parameters studied here. The current AISC design provision over-estimates the design tensile strength of double channel shapes. While, for WT Shapes it under-estimates one. The increase in weld size and decrease in weld length shows slight change in shear lag factor. Comparison is also made with the equation proposed by Fortney and Thornton (2012). The equation under-estimates the design tensile strength of both sections.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (leaves 43-44).
In the recent years, there have been many new skyscrapers built which soar into new heights. The most efficient building system for high-rises has been the framed tube system. However, the framed tube building suffers from shear lag effects which cause a nonlinear distribution of axial stresses along the face of the building. A particular structural system called a diagrid system has caught the attention of the public. The diagrid system is not a new invention. The idea had been around since 1960 and few buildings have been built with the diagrid system. However, the implementation in a larger scale of such tall building was not practical due to high cost related to the difficult node connections. It is only in recent years that the technology has allowed for more reasonable cost of making the diagrid node connections. Despite becoming the new trend in high-rise structures, there are not many technical publications related to diagrid building system. A recent thesis by Moon (2005) studied the various angles of the diagrid to find optimum angle. He has also reviewed the design considerations for diagrid building. This thesis attempts to build on the study by Moon related to the shear lag effect in diagrid building. Diagrid buildings of different configuration are modeled in SAP2000 and analyzed for shear lag effect and structural performance.
by Johan Leonard.
M.Eng.

The effect of thermal-cycling-induced microcracking in fiber-reinforced polymer matrix composites is studied. Specific attention is focused on microcrack density as a function of the number of thermal cycles, and the effect of microcracking on the dimensional stability of composite materials. Changes in laminate coefficient of thermal expansion (CTE) and laminate stiffness are of primary concern. Included in the study are materials containing four different Thornel fiber types: a PAN-based T50 fiber and three pitch-based fibers, P55, P75, and P120. The fiber stiffnesses range from 55 Msi to 120 Msi. The fiber CTE's range from -0.50x10-6/°F to -0.80x10-6/°F. Also included are three matrix types: Fiberite's 934 epoxy, Amoco's ERL1962 toughened epoxy, and YLA's RS3 cyanate ester. The lamination sequences of the materials considered include a cross-ply configuration, [0/90]2s, and two quasi-isotropic configurations, [0/+45/-45/90]s and [0/+45/90/-45]s. The layer thickness of the materials range from a nominal 0.001 in. to 0.005 in. In addition to the variety of materials considered, three different thermal cycling temperature ranges are considered. These temperature ranges are ±250°F, ±150°F, and ±50°F. The combination of these material and geometric parameters and temperature ranges, combined with thermal cycling to thousands of cycles, makes this one of the most comprehensive studies of thermal-cycling-induced microcracking to date.

Experimental comparisons are presented by examining the effect of layer thickness, fiber type, matrix type, and thermal cycling temperature range on microcracking and its influence on the laminates. Results regarding layer thickness effects indicate that thin-layer laminates microcrack more severely than identical laminates with thick layers. For some specimens in this study, the number of microcracks in thin-layer specimens exceeds that in thick-layer specimens by more than a factor of two. Despite the higher number of microcracks in the thin-layer specimens, small changes in CTE after thousands of cycles indicate that the thin-layer specimens are relatively unaffected by the presence of these cracks compared to the thick-layer specimens. Results regarding fiber type indicate that the number of microcracks and the change in CTE after thousands of cycles in the specimens containing PAN-based fibers are less than in the specimens containing comparable stiffness pitch-based fibers. Results for specimens containing the different pitch-based fibers indicate that after thousands of cycles, the number of microcracks in the specimens does not depend on the modulus or CTE of the fiber. The change in laminate CTE does, however, depend highly on the stiffness and CTE of the fiber. Fibers with higher stiffness and more negative CTE exhibit the lowest change in laminate CTE as a result of thermal cycling. The overall CTE of these specimens is, however, more negative as a result of the more negative CTE of the fiber. Results regarding matrix type based on the ±250°F temperature range indicate that the RS3 cyanate ester resin system exhibits the greatest resistance to microcracking and the least change in CTE, particularly for cycles numbering 3000 and less. Extrapolations to higher numbers of cycles indicate, however, that the margin of increased performance is expected to decrease with additional thermal cycling. Results regarding thermal cycling temperature range depend on the matrix type considered and the layer thickness of the specimens. For the ERL1962 resin system, microcrack saturation is expected to occur in all specimens, regardless of the temperature range to which the specimens are exposed. By contrast, the RS3 resin system demonstrates a threshold effect such that cycled to less severe temperature ranges, microcracking does not occur. For the RS3 specimens with 0.005 in. layer thickness, no microcracking or changes in CTE are observed in specimens cycled between between ±150°F or ±50°F. For the RS3 specimens with 0.002 in. layer thickness, no microcracking or changes in CTE are observed in specimens cycled between ±50°F.. Results regarding laminate stiffness indicate negligible change in laminate stiffness due to thermal cycling for the materials and geometries considered in this investigation. The study includes X-ray examination of the specimens, showing that cracks observed at the edge of the specimens penetrate the entire width of the specimen. Glass transition temperatures of the specimens are measured, showing that resin chemistry is not altered as a result of thermal cycling.

Results are also presented based on a one-dimensional shear lag analysis developed in the literature. The analysis requires material property information that is difficult to obtain experimentally. Using limited data from the present investigation, material properties associated with the analysis are modified to obtain reasonable agreement with measured microcrack densities. Based on these derived material properties, the analysis generally overpredicts the change in laminate CTE. Predicted changes in laminate stiffness show reasonable correlation with experimentally measured values.
Ph. D.

Adhesive bonding is a common, robust, and inexpensive method of joining materials. Of particular interest is the behavior under shear loading, where adhesive bonding excels compared to alternative joining methods. However, while the quasi-static response of these joints is well understood, the dynamic behavior is largely unknown.

To this end, a series of experiments were devised and performed where two bars are adhesively bonded using a simple lap joint and subjected to a high-speed impact from a steel slug. These tests were configured to, as much as possible, isolate the type of wave that generates adhesive shear and minimize the effect of reflected and induced waves. While keeping the overall geometry constant, the adhesive material, substrate material, and projectile velocity were varied.

The wave behavior was recorded using surface-mounted strain gages. Also, digital image correlation techniques were developed to analyze high-speed video of the impact event. From these experiments, a number of useful measures can be extracted, including the critical input (projectile) kinetic energy and the specific energy absorbed by the adhesive.

The techniques developed in this thesis allow for the suitability of different substrate/adhesive combinations under ballistic shear impact to be quantitatively evaluated.

Additionally, dynamic plate theory is used to derive an analytical model of the substrate/adhesive system. Several solutions to this model which were solved using a Finite Difference approach are included. These solutions were then compared to the strain histories recorded in the physical experiments.

Fiber-metal laminates (FML) are the advanced materials that are developed to improve the high performance of lightweight structures that are rapidly becoming a superior substitute for metal structures. The reasons behind their emerging usage are the mechanical properties without a compromise in weight other than the traditional metals. The bond remains a concern. This thesis reviews the effect of pre-treatments, say heat, P2 etch and laser treatments on the substrate which modifies the surface composition/roughness to impact the bond strength. The constituents that make up the FMLs in our present study are the Aluminum 2024 alloy as the substrate and the carbon fiber prepregs are the fibers. These composite samples are manufactured in a compression molding process after each pre-treatment and are then subjected to different tests to investigate its properties in tension, compression, flexural and lap shear strength. The results indicate that heat treatment adversely affects properties of the metal and the joint while laser treatments provide the best bond and joint strength.

In this document, an experimentation on composite materials (Fiber Reinforced Cementitious Matrix FRCM and Fiber Reinforced Polymer FRP) applied on a masonry substrate has been described. 38 Single-lap Shear tests were carried out on steel reinforced specimens with different matrix widths (SRG) and with different types of degradation due to conditioning cycles (SRG, SRP) in order to investigate the failure and transfer mechanisms between the composite and the substrate.

Two failure mechanisms in a double lap joint are investigated. Analytical models of net-section and gross-section failure modes are proposed to describe these mechanisms. The effects of lamping force, interference fit, maximum axial load and WDCP on fatigue performance of the joint are included in the models. The effect of WDCP is assumed to give a reduction in friction coefficient. Three types of stress reduction factors are proposed in the net-section failure model to account for these parameters. The stress reduction factors modify stress range that is used in crack growth calculation. If there are no effects of these parameters, the stress reduction factors are equal to one. Two types of fretting stress are introduced in gross-section failure model to describe either sliding contact or incipient sliding contact on faying surface. The fretting stress is combined with body stress to modify stress range. The net-section failure model predicts that fatigue life is increasing as interference fit, clamping force and friction coefficient increase. The gross-section failure model predicts that fatigue life is decreasing as clamping force and friction coefficient increase. Both models predict that fatigue life is decreasing as maximum axial load increases. Transition of the failure mode occurs earlier as friction coefficient and interference fit increase, while it is delayed as maximum axial load increases. A transition parameter is proposed to establish a relationship between the four main parameters. The transition parameter is expressed in a polynomial equation. It gives an optimum combination of the four main parameters in order to achieve relatively higher fatigue life by having gross-section failure mode. Finite element analysis and fatigue testing are performed to validate the models. The finite element and the analytical models show that stress concentration factor at the edge of the hole is decreasing as clamping force increases. The rate of decrease of stress concentration factor is increasing as friction coefficient increases. While stress concentration factor on the faying surface is increasing as clamping force and friction coefficient increase. Fatigue testing reveals that the fatigue life of the joint is in good agreement with the predicted fatigue life of the proposed models.

Les Bétons Fibrés à Ultra hautes Performances (BFUP) se caractérisent par une résistance en compression bien supérieure à celle des BTHP couverts par la normalisation, une excellente durabilité et l'emploi d'un assez fort taux de fibres métalliques modifiant le recours habituel aux armatures. Ils sont notamment marqués par une résistance à la traction élevée. Cependant, selon le pourcentage volumique et le(s) type(s) de fibres initialement prévus dans la formulation et l'orientation réelle des fibres dans la structure vis-à-vis des directions principales de traction, leur comportement en traction peut être adoucissant ou écrouissant. Ces deux comportements nécessitent une approche différente pour assurer la sécurité du dimensionnement. Dans un premier temps, des méthodes de caractérisation du comportement en traction des BFUP ont été mises au point de manière à déterminer quel comportement va se mettre en place pour un BFUP et un élément structurel donné, en s'appuyant sur l'essai de flexion quatre points réalisé sur éprouvette non-entaillée. Cet essai nécessite l'utilisation d'une analyse inverse afin d'obtenir la loi de comportement " contrainte-déformation " (dans le cas d'un BFUP écrouissant en traction directe) ou " contrainte-ouverture de fissure " (dans le cas d'un BFUP adoucissant en traction directe). La configuration de l'essai de flexion quatre points pouvant entraîner des artefacts, elle nécessite un raccordement avec l'essai de traction directe. Pour valider ce raccordement, une méthode d'essai permettant de tester des corps d'épreuve de dimensions identiques en flexion et en traction directe a été mise au point. Les résultats de l'analyse inverse des essais de flexion ont été comparés à ceux des essais de traction directe. La comparaison a notamment permis de démontrer la robustesse des méthodes d'analyse proposées en particulier vis-à-vis de la cohérence de la discrimination écrouissant/adoucissant à partir du relevé de fissures sur chaque éprouvette. Dans un second temps, des méthodes de calcul adaptées à une approche type " contrainte - ouverture de fissure " ou " contrainte - déformation " ont été testées ou développées afin de prédire la résistance ou le comportement des poutres en BFUP soumises à des sollicitations concomitantes de flexion et d'effort tranchant. Cette configuration de sollicitation fait en effet intervenir de façon critique le comportement en traction du matériau. Pour valider ces méthodes de calculs, onze poutres en BFUP armé ou précontraint, avec ou sans armatures transversales et avec ou sans fibres (métalliques ou organiques) ont été testées sous une configuration de flexion conduisant à une rupture par effort tranchant. La caractérisation simultanée du comportement mécanique des BFUP à l'échelle du matériau en prenant en compte l'orientation réelle des fibres au sein des poutres, qui constitue une originalité de ce programme, s'est avérée particulièrement importante pour constater l'interaction entre le matériau, la géométrie de la structure et le procédé de mise en œuvre du BFUP sur l'orientation des fibres. Les méthodes d'analyse des essais de flexion quatre points mises au point ont permis d'évaluer quantitativement l'influence de la structure sur les paramètres caractérisant le comportement en traction du BFUP, notamment la déformation correspondant à la localisation de la fissure et marquant la fin du comportement global " pseudo-plastique ". Les conditions de synergie d'éventuelles armatures transversales et du BFUP vis-à-vis de la résistance à l'effort tranchant, ont pu être mises en évidence. Pour étendre l'analyse, la capacité de l'approche en " contrainte - ouverture de fissure " à prédire la résistance de poutres soumises à des sollicitations concomitantes de flexion et d'effort tranchant a été testée. L'approche en " contrainte - déformation " a également été appliquée, contribuant au développement et à la validation de méthodes élastoplastiques adaptées aux BFUP

碩士
朝陽科技大學
營建工程系碩士班
89
Due to the variety of cross sectional shape for cold-form steel members, for the practice reason it is not normally possible or convenient to connect each element to the end connection. Therefore, the shear lag effect will be occurred for the member subjected to tension. This effect reduces the strength of the member because the stresses distributed in the entire section are not uniform. It is found that the design formulas for calculating the cold-formed steel tension members according to most specifications of several countries do not consider the shear lag effect. Therefore, this study is concentrated on the investigation of the shear lag effect on the cold-formed steel tension members. Channel specimens with different dimensions tested by using bolted connection were discussed in this study. The comparison was also made between the test results and predictions computed based on several specifications. In order to study the stress distribution in the various location of any cross section of specimen, the finite-element software ANSYS was also conducted in this research. Base on the experimental results, it was found that the tension strengths of test specimens predicted by the AISC-Code (1993), which takes account of shear lag effect, are more closely to the test values. The predictions according to AISI-Code (1996) and AS/NZS 4600 Code (1996) seem to be overestimated as compare to the test results. It is also noted that there are quite discrepancy between the test results and the values predicted by British Standard (1998) and LaBoube recommended equation.

碩士
朝陽科技大學
營建工程系碩士班
89
Abstract The currently design method of bolt connections for cold-formed steel members was briefly introduced in this research. Comparisons of design criteria were made between the United States Standard, Australia Standard, British Standard, and other researcher’s recommendations in this study. This research’s result could be used to establish the design regulation of cold-formed steel construction in domestic specification. This study is concentrated on the investigation of the shear lag effect on the cold-formed steel tension members. L-shaped specimens with different dimensions tested by using one-line or two-line bolted connections were discussed in this study. Based on the experimental results, it was found that there are quite discrepancy between the test results and the predicted values for the specimens with larger size of non-connected element. It is also noted that the member fracture failure mode was found in most two-line bolted connection specimens, and the plate end fracture failure or plate bearing failure were found in most one-line bolted connection specimens.

Post-earthquake examinations of reinforced concrete structures often show structural damage resulting from bond and shear failures. Such failures typically occur in reinforced concrete elements with details known to cause problems, such as widely spaced transverse reinforcement and/or lap splices located in regions of flexural yielding. These details are common in older reinforced concrete buildings (built before 1970) that have reinforced concrete columns with longitudinal reinforcement spliced just above the floor level, and transverse reinforcement spaced at a distance of d/2 or longer. This investigation focused on means to increase the deformability of existing reinforced concrete elements susceptible to bond and shear failures during a seismic event or other applications requiring toughness. The effects of confinement provided by epoxied anchors, spiral transverse reinforcement, and post-tensioned external clamps were investigated. Emphasis was placed on producing a strengthening device that can be sized, fabricated, and installed with ease because most of the existing strengthening techniques require specialized labor, tools, and materials. The observations collected support the idea that active confinement provided by post-installed and post-tensioned transverse reinforcement was the most effective method to improve structural deformability among the methods studied and within the ranges considered.