Search

Earthquake causes severe damage to buildings and infrastructure, due to not only the ground motion but also secondary actions, such as impact, blast and fire which would occur after an earthquake. In order to investigate the post-earthquake loading scenarios, it is important to assess the partial damage of structures caused by earthquake. This paper presents the behavior of double-angle bolted steel I-beam to hollow square tubular column connections under static and cyclic loading. A detailed experimental study is presented in which two groups of bolted steel connections with different column wall thickness are considered. The flexibility and strength of the connections are measured, while the damage phenomena and failure modes are explored in the tests. The connection damage under cyclic loading is found to be an accumulative developing process of fracture which leads to significant gradual degradation of the mechanical properties of the connections. Quantitative evaluations of the cyclic loading induced damage are carried out to investigate the damage level of connections according to different loading scenarios. The test results herein provide a detailed understanding of the behavior of the double-angle bolted connections under seismic loading, which would be useful for further investigations under post-earthquake actions. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of the bond strength between carbon fiber reinforced polymer (CFRP) and steel substrate by utilizing the pull-off test and scanning electron microscope (SEM) analysis. A series of pull-off experiments was conducted by using three types of CFRP (CFRP sheets and CFRP laminates with/without woven mesh) and two types of epoxy adhesive (ductile and brittle epoxy adhesive) with/without carbon nanotube (CNT) modification. Pull-off samples with CFRP laminates possess higher (about double) bond strength than that of samples with CFRP sheets, due to the good saturation of fibers in the laminates. The steel-CFRP bond with ductile epoxy adhesive (Araldite 2011) is found to have about 16% higher bond strength when compared to that of brittle epoxy (MBrace Saturant), even though the tensile strength of Araldite 2011 is about 40% less than that of MBrace Saturant. Also, it is shown that modified epoxy with CNTs is more efficient than neat epoxy for bonding CFRP to steel at a moderately elevated temperature, and increasing the bond strength about twofold. [ABSTRACT FROM AUTHOR]

Earthquake causes wide and severe damage to building structures, due to not just the great ground motion but also secondary actions, such as impact, blast or fire, occurring after earthquake. The extreme combined loading scenario should be considered for safety of buildings and lives. Taking fire for example, the combined load can be considered as an event in which the structures are first partially damaged under an earthquake and then attacked by fire. In order to investigate the post-earthquake loading scenario, it is important to assess the partial damage caused by earthquake on different components of structures. The behavior of welded steel I-beam to hollow square tubular columns is investigated herein. A detailed experimental study is presented in which two groups of unstiffened welded steel connections, with the same configurations, subjected to static and cyclic loading are considered. The flexibility and strength of the connections are measured, while the damage phenomena and failure modes are explored during the tests. The connection damage is found to be a cumulative fracture developing process which leads to significant gradual degradation of the mechanical properties of the connection. The quantificational evaluations of the cyclic loading induced damage are also carried out to investigate the connection damage level according to different loading intensities. A finite element modeling numerical study is also carried out to validate the experimental results and a good agreement is achieved. The test results and FE modeling provide a benchmark data for the unstiffened welded connections and can be used for further investigations of the connections subjected to combined actions such as post-earthquake fire. [ABSTRACT FROM AUTHOR]

Strengthening steel structures using carbon fiber reinforced polymer (CFRP) materials has attracted much attention in recent years owing to their potential for fatigue crack repair and their convenience in construction. However, little is known about the efficiency of this strengthening method when applied to steel plates at different crack propagation stages. An experimental study was carried out on notched steel plates strengthened using CFRP laminates. 20 specimens were tested to evaluate the fatigue performance of the strengthened steel plates with emphasis on various degrees of initial damage, simulated by different lengths of slots, including 2%, 10%, 20%, 30% and 40% of the plate width. The effects of the retrofitted configuration and CFRP stiffness were also investigated. The "beach marking" technique and crack propagation gauges were adopted to monitor the fatigue crack propagation. The experimental results were very encouraging, demonstrating that the CFRP patches could effectively slow crack growth and extend fatigue life, regardless of the initial damage levels. More effective strengthening was found by using ultra-high modulus CFRP laminates, covering the initial cracks with CFRP and repairing at an earlier stage (i.e. smaller damage level). [ABSTRACT FROM AUTHOR]

Advanced carbon fiber reinforced polymer (CFRP) demonstrates promise for the fatigue strengthening of steel structures. By decreasing the stress field at the crack tip, the stress intensity factors (SIFs) can be effectively reduced by CFRP reinforcement. In this paper, the mode I SIF of CFRP-reinforced center-cracked tensile (CCT) steel plate is proposed based on a series of fatigue tests. The selected fatigue tests include experiments conducted by the authors as well as fatigue tests reported in the literature, covering different CFRP systems (low/high modulus, CFRP sheeting/plate) with various CFRP strengthening dimensions. The classical mode I SIF of CCT steel plate without CFRP strengthening is selected as the basis of the proposed solution. Then two reduction factors, similar to the correction factors given in the Japanese Society of Steel Construction (JSSC) standard, are introduced to study the effects of the mechanical properties of CFRP composites and the geometries of the CFRP reinforcement, respectively. Modified SIFs for both single-side CFRP-reinforced and double-side CFRP-reinforced CCT steel plates are proposed. It is found that the experimental SIFs of CFRP-reinforced CCT steel plates can be reasonably captured by the proposed mode I SIF formula. Finally, parametric studies for investigating the sensitivity of SIF to various mechanical and geometric factors are presented. [ABSTRACT FROM AUTHOR]

Cracked cross-beam connections made of thin-walled rectangular hollow sections (RHS) are repaired with carbon fiber-reinforced polymer (CFRP) sheets. Constant amplitude fatigue experiments are conducted on the repaired specimens. A pilot test is conducted on a T-connection of square hollow sections (SHS) to explore the effective method of applying CFRP. Due to the peeling effect at the corner region of the SHS-to-SHS connection, early debonding happens in the pilot test that only results in a slight extension in fatigue life. In the following experiments of repairing RHS-to-RHS cross-beam connections, circumferential or transverse restraining CFRP patches are applied in the corner region that prevents early debonding successfully and leads to significant increase in fatigue life. Finally, an improvement is made with the addition of steel strengthening plates that increase both the flexural stiffness and fatigue life of the cracked specimens significantly. The proposed retrofitting method may be useful for repairing other similar fatigue-cracked welded tubular connections. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study on the use of carbon fiber-reinforced polymer (CFRP) sheets to strengthen non-load-carrying cruciform welded joints subjected to fatigue loading. Failure modes and corresponding fatigue lives were recorded during tests. Scatter of test results was observed. Thereafter, a series of numerical analyses were performed to study the effects of weld toe radius, the number of CFRP layers and Young's modulus of reinforced materials on local stress concentration at a weld toe. It was found that fatigue life of such welded connections can be enhanced because of the reduction of stress concentration caused by CFRP strengthening. Parametric study indicates that the weld toe radius and the amount of CFRP are the key parameters influencing the stress concentration factors and stress ranges of the joint. Enhancement of modulus for adhesive and CFRP sheets can also be beneficial to the fatigue performance to some extent. [ABSTRACT FROM AUTHOR]

This paper clarifies the terminologies used to describe the size effect on fatigue behavior of welded joints. It summarizes the existing research on size effect in the perspective of newly defined terminologies. It identifies knowledge gaps in designing tubular joints using the hot spot stress method, i.e. thin-walled tubular joints with wall thickness less than 4 mm and thick-walled tubular joints with wall thickness larger than 50 mm, or diameter to thickness ratio less than 24. It is the thin-walled tubular joints that are addressed in this paper. It is found that thin-walled tube-plate T-joints do not follow the conventional trend: the thinner the section is, the higher the fatigue life. It is also found that simple extrapolation of existing fatigue design curves may result in unsafe design of thin-walled tube–tube T-joints. The effect of chord stiffness on fatigue behavior of thin-walled tubular T-joints is also discussed. [ABSTRACT FROM AUTHOR]

The fatigue behavior of welded thin-walled T-joints made up of both circular hollow section (CHS) braces and chords, subjected to cyclic in-plane bending, is described in this paper. CHS chords and braces are of thicknesses less than 4 mm. Current fatigue design guidelines show that the design of welded tubular nodal joints is restricted to thicknesses greater than or equal to 4 mm. The increased availability and use of thin-walled (t<4 mm) tubes of high-strength steels in recent years, in structures subjected to cyclic loading, means that it is important to study the fatigue behavior of welded thin-walled tubular nodal joints. In this paper, welded thin-walled CHS-CHS T-joints subjected to constant-stress-amplitude cyclic in-plane bending range are studied. The stress concentration factors (SCFs) determined experimentally at the brace and chord crown positions are shown to be about 30% and 40% respectively of the SCFs determined using parametric equations in existing fatigue design guidelines. The fatigue tests showed that in welded thin-walled CHS-CHS T-joints, a through-thickness crack occurs when the surface crack length along the weld toes in the chord has grown to a length equal to about 40% of the circumference of the brace member. An end of test failure criterion was proposed as an alternative to the through-thickness failure criterion, in obtaining data that is suitable for determining fatigue design S-N curves. [ABSTRACT FROM AUTHOR]

No abstract received. [ABSTRACT FROM AUTHOR]