I-shaped Steel Research Articles

Piezoelectric sensing and non-parametric statistical signal processing for health monitoring of hysteretic dampers used in seismic-resistant structures

The paper proposes a new application of non-parametric statistical processing of signals recorded from vibration tests for damage detection and evaluation on I-section steel segments. The steel segments investigated constitute the energy dissipating part of a new type of hysteretic damper that is used for passive control of buildings and civil engineering structures subjected to earthquake-type dynamic loadings. Two I-section steel segments with different levels of damage were instrumented with piezoceramic sensors and subjected to controlled white noise random vibrations. The signals recorded during the tests were processed using two non-parametric methods (the power spectral density method and the frequency response function method) that had never previously been applied to hysteretic dampers. The appropriateness of these methods for quantifying the level of damage on the I-shape steel segments is validated experimentally. Based on the results of the random vibrations, the paper proposes a new index that predicts the level of damage and the proximity of failure of the hysteretic damper.

Innovative steel bridge girders with tubular flanges

I-shaped steel girders with tubular flanges have been studied for application in highway bridges because of their large torsional stiffness compared to conventional I-shaped steel plate girders (I-girders). For straight girder bridges, the large torsional stiffness of a tubular flange girder (TFG) results in significantly greater lateral–torsional buckling strength compared to a corresponding I-girder. For horizontally curved girder bridges, the large torsional stiffness of a TFG results in much less normal stress, vertical displacement and cross-sectional rotation compared to a corresponding I-girder. The paper presents experimental and finite element analysis results for straight and horizontally curved TFG bridges. The results show the advantages of TFGs in comparison to conventional I-girders. A TFG demonstration bridge constructed in the USA is described.

Tangent moduli of hot-rolled I-shaped axial members considering various residual stress distributions

This paper presents an equation for the effective tangent moduli for steel axial members of hot-rolled I-shaped section subjected to various residual stress distributions. Because of the existence of residual stresses, the cross section yields gradually even when the member is subjected to uniform axial stresses. In the elasto-plastic stage, the structural response can be easily traced using rational tangent modulus of the member. In this study, the equations for rational tangent moduli for hot-rolled I-shaped steel members in the elasto-plastic stage were derived based on the general principle of force-equilibrium. For practical purpose, the equations for the tangent modulus were presented for conventional patterns of the residual stress distribution of hot-rolled I-shaped steel members. Through a series of material nonlinear analyses for steel axial members modeled by shell elements, the derived equations were numerically verified, and the presented equations were compared with the CRC tangent modulus equation, the most frequently used equation so far. The comparative study shows that the presented equations are extremely effective for accurately analyzing elasto-plastic behavior of the axially loaded members in a simple manner without using complex shell element models.

Plastic coupled instabilities of I-shaped steel beams

The paper presents the case of plastic instability of I-shaped beams where the rotation capacity is a very important characteristic in order to assure the required ductility in plastic or seismic design. The failure of such beams can be due to the local plastic plate buckling of compression flange and local plate buckling of the web in flexural compression, produced in-plane or out-of-plane. In the same time the failure can occurs by coupling of these two local buckling modes. In order to study the plastic buckling of beams and to determine the available rotation capacity which is required by the plastic or seismic design, the collapse plastic mechanism theory was developed and a specialized computer program DUCTROT-M was elaborated. The parametrical analysis reveals the paramount importance of the web to thickness ratio and furthermore the sensitivity in out-of-plane buckling of the European hot-rolled sections.

A new scheme for the seismic retrofit of multi-span simply supported bridges

There are two alternative strategies that a designer may adopt and combine when faced with the retrofitting of a bridge: (a) the increase in the capacity or (b) the reduction in the actions of the structure. In this article, a new scheme, based on the second strategy, is proposed for the retrofit of existing multi-span simply supported (MSSS) bridges. The reduction in the actions of the bridge was mainly achieved by utilising an external restraining system consisting of I-shaped steel piles driven in the backfill soil and a slab that is the pile-cap of the piles. The restraining system was preliminarily designed and assessed in an existing MSSS bridge system, whose deck slab was made continuous. The existing and the retrofitted bridge were analysed by means of non-linear dynamic time history analysis and their response was compared in terms of serviceability and earthquake resistance performance. The study showed that the retrofitting scheme enhanced effectively the earthquake resistance of the existing bridge.

Experimental investigation on fatigue behavior of steel reinforced concrete composite beam-to-girder joints

Fatigue behavior and failure mechanism of steel reinforced concrete (SRC) beam-to-girder joints is discussed in this paper, which is intended for use in high-speed railway station structures due to their high stiffness and load capacity. Three identical SRC beam-to-girder joint specimens were designed and tested under static loading and two stages of fatigue loading. In the first stage of fatigue loading, the specimens were subjected to design fatigue load for 2 million cycles, while during the second stage, the specimens were loaded to failure under increased fatigue loading amplitude in order to know its fatigue strength and failure mechanism. The constructional details of SRC beam-to-girder joint specimen and the method of loading and testing are presented. The comparison in structural behavior of the joint is made between under static and fatigue loading. Fatigue failure characteristics of the joint are described in detail. It is found that the SRC beam-to-girder joints remained in their elastic range and the concrete surface crack did not exceed 0.1 mm when subjected to design static loading and 2 million cycles of design fatigue loading. There was no significant difference in structural behavior of each component of SRC composite beam between static and fatigue loading. Fatigue failure occurred after these joints were applied higher-level fatigue loading for another 0.70 to 0.91 million cycles. Fatigue crack was initiated at the tension flange of I-shape steel of beam connected by welding to the flange of I-shape steel of girder or at the hole in tension flange of I-shape steel of beam, and then the crack propagated along flange width and web height of the I-shape steel in beam until the I-shape steel lost loading capacity due to lack of enough cross section. The fatigue behavior of constructional detail of the I-shape steel played a key role in the fatigue strength of the SRC beam-to-girder joints. Discussions on improving the fatigue strength of SRC beam-to-girder joints and future research aspects are presented finally.

Interfacial behavior of mechanically anchored FRP laminates for strengthening steel beams

This study investigates the response of FRP–steel anchored lap connections along with the associated interfacial behavior. The investigation is conducted experimentally and numerically. The experimental program includes testing of eighteen short specimens to explore the influence of sheared edge distance and rolled edge distance on the load carrying capacity and ductility of the assembly. In addition, six longer connections are tested to assess the effect of the spacing between bolts on the response. The findings suggest a sheared edge distance of about six to seven times the bolt hole's diameter. The effect of the rolled edge distance values considered in the study on the performance of the connections is found to be insignificant. A non-linear load–slip model is proposed to simulate the interfacial behavior of the assembly. A finite element study is conducted using an equivalent non-linear spring element to simulate the interfacial behavior based on the proposed load–slip model. The excellent match between displacement and strain responses measured experimentally and their numerical predictions validates the accuracy of the proposed load–slip model. The flexural behavior of two full-scale I-shaped steel beams is then investigated experimentally to explore the enhancement in the response of beams strengthened with mechanically anchored FRP laminates. Finally, a finite element model is utilized to predict the elasto-plastic response of the tested steel beams. The excellent agreement between the numerical predictions and experimental measurements provides another validation for the proposed load–slip model.

철도교량 구조형식별 감쇠비 하한값 산정을 위한 시험적 연구

철도교량 동적 설계 및 동적 안전성을 해석적으로 평가하기 위해서는 교량의 감쇠비를 산정하는 것이 매우 중요하다. 본 연구에서는 국내 고속 및 일반철도에서 일반적으로 사용되고 있는 소수주형강합성교, PSC Box, Steel Box, PSC, IPC, Precom, Preflex에 대하여 실내 모형실험 및 운행 중 현장계측을 하였다. 이러한 고속 및 일반철도의 대표적 교량형식에 대한 실내외 시험을 통해 대수감소율을 적용하여 감쇠비를 분석하였다. 따라서 철도교량의 감쇠비는 하중크기, 가진주파수, 진폭에 영향을 받지 않는 것으로 분석되었다. 또한, 기존 철도설계기준에 제시된 감쇠비 하한치와 비교하여 PSC구조 및 강합성구조 철도교량의 경우 감쇠비 하한값을 1.0%로 적용하는 것이 합리적이라 판단되었다. The damping ratio of railway bridge has become one of the most important issues in dynamic design and dynamic stability of railway bridge. In the present study, laboratory and field test were performed for railway bridges such as a twin I-shaped steel composite girder, PSC box, steel box, PSC, IPC, PRECOM, preflex. The damping ratio of railway bridge according to structure types was estimated by logarithmic decrement method. Therefore, magnitude, frequency and amplitude of load did not affect damping ratio of railway bridge. Also, damping ratio limit of steel composite and PSC bridges was evaluated in 1.0%.

Accordion effect of prestressed steel beams with corrugated webs

Various types of composite members have been developed to utilize the combined advantages of existing reinforced concrete and steel structures, and to actively improve ductility and serviceability of structural members. One of them is the hybrid-type steel beam, in which the prestressing method is applied to a steel beam. Introducing prestress to the existing I-shaped steel beam, however, results in a very low prestress efficiency due to the large axial stiffness of the section. On the other hand, if corrugated webs are used, the prestress introduced to the main flexural-resistant elements—the upper and lower flanges—gets larger due to the accordion effect, so that it is very advantageous not only in terms of serviceability, but also of achieving the improved flexural strength. Most previous studies on steel members with corrugated webs, however, have focused on the shear buckling strength of the corrugated webs, and few studies have been conducted on the accordion effect of the corrugated webbed beam to which prestress is introduced. Therefore, this research proposed two rational and theoretical models to quantitatively estimate the accordion effect, which is induced by the introduction of prestress to corrugated webbed steel beams, and performed experiments on two steel beams with corrugated webs and one with typical wide flange section. The experimental results showed that the prestressing efficiency of steel beams with corrugated webs increased more significantly than that of the steel beam with a typical web, and it is verified that the proposed methods are very simple and provide good agreements with the experimental results.

Mechanical Properties of Reinforced Steel Beams Influenced by the Degree of Unloading

Several I-shaped steel beams reinforced by CFRP are unloaded at different levels and the mechanical properties are analyzed and compared. Five forms of I-shaped steel beam (beam without reinforced; reinforced beam in condition of non-unloading; reinforced beam in condition of 50% unloaded; reinforced beam in condition of 75% unloaded; reinforced beam in condition of completely unloaded) are analyzed and compared. Conclusions are made that the stiffness and yielding load of I-shaped steel beams reinforced by CFRP are improved and the bearing capacity is improved for certain degree when the beams are unloaded.

Spindle position control by embedded electromagnetic poles

A novel embedded cylindrical-array magnetic actuator (ECAMA) is proposed and verified by experiments to provide sufficient magnetic force for spindle deviation regulation of high-speed milling process. Four I-shape silicon steel columns enclosing the spindle constitute the backbone of the ECAMA. The shape of modified concave-type yokes is designed to reduce the average air gap between magnetic poles and the spindle. In contrast to the conventional AMB (active magnetic bearing) design for which coils are usually wound on the yokes, the copper wire is wound on the I-shape silicon steel columns. As a result, the overall wound coil turns can be much increased. In other words, stronger magnetic force can be induced by ECAMA. On the other hand, to reduce the cost of ECAMA, two pairs of self-sensing modules are employed to replace the gap sensors for measurement of spindle position deviation. In order to verify the efficacy of the proposed ECAMA and the self-sensing module, high-speed milling tests are undertaken. By inspection on the precision and quality of the finish surface of workpiece, the superiority of ECAMA and the self-sensing module are assured.

Regulation of spindle position by magnetic actuator array

A novel embedded cylindrical-array magnetic actuator (ECAMA) is proposed and verified by experiments to provide sufficient magnetic force for spindle deviation regulation of high-speed milling process. Four I-shape silicon steel columns enclosing the spindle constitute the backbone of the ECAMA. The shape of modified concave-type yokes is designed to reduce the average air gap between magnetic poles and the spindle. In contrast to the conventional AMB (active magnetic bearing) design for which coils are usually wound on the yokes, the copper wire is wound on the I-shape silicon steel columns. As a result, the overall wound coil turns can be much increased. In other words, stronger magnetic force can be induced by ECAMA. On the other hand, to reduce the cost of ECAMA, two pairs of self-sensing modules are employed to replace the gap sensors for measurement of spindle position deviation. In order to verify the efficacy of the proposed ECAMA and the self-sensing module, high-speed milling tests are undertaken. By inspection on the precision and quality of the finish surface of workpiece, the superiority of ECAMA and the self-sensing module are assured.

Finite element analysis of curved steel girders with tubular flanges

A tubular flange girder is an I-shaped steel girder with either rectangular or round tubes as flanges. A tubular flange girder has a much larger torsional stiffness than a conventional I-shaped plate girder and less potential for cross section distortion than a box-girder, and is, therefore, an interesting alternative girder for horizontally curved steel bridges. Finite element (FE) models of curved tubular flange girders are presented in this paper, considering material inelasticity, second-order effects, initial geometric imperfections, and residual stresses. A parametric study is performed using the FE models to study the effects of stiffeners, tube diaphragms, geometric imperfections, residual stresses, and cross section dimensions on the load capacity of curved tubular flange girders. Finally, the FE results for curved tubular flange girders are compared with results for corresponding curved I-shaped plate girders, and the advantages of tubular flange girders are summarized.

Behavior of Hollow Tubular-Flange Girder Systems for Curved Bridges

This paper describes research results for an innovative curved highway bridge girder system, which uses I-shaped steel girders with hollow rectangular tubes as flanges. The increased torsional stiffness provided by the tubular flanges dramatically improves the structural behavior of the curved girders, resulting in substantially reduced deflection, cross section rotation, and stress compared to conventional curved I-shaped steel plate girders. In this paper, finite-element (FE) models for systems of curved tubular-flange girders are described. The models consider material inelasticity, second-order effects, initial geometric imperfection, and residual stresses. The girder systems are comprised of curved hollow tubular-flange girders (CHTFGs), cross frames between the CHTFGs, and a concrete deck. A parametric study is performed using the FE models to study the effects of web stiffeners, tube diaphragms, geometric imperfection, and residual stresses on the load capacity of three-girder systems with CHTFGs. Then, the results for the CHTFG systems are compared with results for corresponding conventional curved I-girder systems. The effects of the curvature, cross section dimensions, number of cross frames, and a concrete deck are investigated. The results indicate that the CHTFG systems are more structurally efficient than the corresponding curved I-girder systems.

Major-axis elastic buckling of axially loaded castellated steel columns

Perforated-web steel sections have been used as structural members since the Second World War in an attempt to enhance the flexural behavior without increasing the cost of the material. Nowadays, such sections are widely used in a variety of geometries suitable for various loading conditions. In the current study, the finite element method is used to investigate the major-axis buckling characteristics and associated buckling capacity of axially loaded I-shaped steel columns. Extensive numerical analyses are conducted to evaluate the reduction in buckling capacity of castellated columns due to shear and flexural deformations. Obtained results are used to identify a dimensionless buckling modification factor, η, and the associated equivalent section properties that can be implemented to assess the critical buckling load of the considered columns. The study considers a wide range of practical geometric dimensions, as well as, various columns’ end conditions. A simplified procedure is suggested to evaluate the buckling capacity of castellated columns. Charts are developed to enable practitioners to readily estimate the buckling load of such a type of castellated columns more accurately.

Study on Calculation Methods for Ultimate Moment Capacity of SRC Columns with T-Shaped Steel

Based on the common calculation methods of normal section bearing capacity of steel reinforced concrete (SRC) columns with I-shaped steel, SRC columns containing T-shaped steel are presented and their mechanical properties and failure modes are analyzed. Combining with actual engineering and current national codes, the calculation methods and formulas of ultimate moment capacity of this column are proposed and heights of the concrete pressured region in two different situations are compared, by which it can be seen that SRC columns are easier to form large eccentric compression failure when the big flange is nearer to axial force N .The bearing capacity of one SRC column with T-shaped steel is checked using above proposed formulas and the calculation results agree well with the experimental data, and finally this numerical example shows that the suggested method has good precision and reasonable application.

Lateral Torsional Buckling Strength of Tubular Flange Girders

I-shaped steel girders with tubular flanges have been studied for application in highway bridges because of their large lateral torsional buckling (LTB) strength relative to conventional I-shaped steel plate girders. This paper discusses the LTB strength of tubular flange girders, focusing on concrete-filled tubular flange girders (CFTFGs) where the concrete-filled tube is the compression flange. Using finite-element (FE) models of CFTFGs, a parametric study was conducted to investigate the influence of girder geometry and material strength on the LTB strength. Design flexural strength formulas, considering LTB, for construction conditions and for ultimate strength in the final constructed condition, were developed based on the results of the parametric study. These formulas estimate the LTB strength of CFTFGs that are perfectly braced laterally and torsionally at brace points. A similar FE study of conventional I-girders was conducted and the results are compared with those of CFTFGs.

Flexural strength of tubular flange girders

A tubular flange girder is an I-shaped steel girder with either rectangular or round tubes as flanges. A tubular flange girder has a much larger torsional stiffness than a conventional I-shaped plate girder of similar weight, which results in a much larger lateral–torsional buckling strength. Finite element (FE) models of tubular flange girders with hollow tubes (HTFGs) are developed in this paper, considering material inelasticity, instability, initial geometric imperfections, and residual stresses. A parametric study is performed using the FE models to study the effects of stiffeners, geometric imperfections, residual stresses, cross section dimensions, and bending moment distribution on the lateral–torsional buckling flexural strength of HTFGs. These analytical results are used to evaluate formulas for determining the flexural strength of HTFGs.

Experimental Study of Tubular Flange Girders

The behavior of I-shaped steel girders with flanges made from concrete-filled tubes is investigated experimentally, focusing on concrete-filled tubular flange girders (CFTFGs) in positive bending regions where the concrete-filled tube is the compression flange. The investigation included CFTFGs that are either composite or noncomposite with a concrete deck. For the composite CFTFGs, girders with rectangular tubes and either a flat web or a corrugated web are studied, and for the noncomposite CFTFGs, girders with round tubes and flat webs are studied. The objectives are: (1) to provide experimental data demonstrating the load carrying capability of CFTFGs and the advantages of CFTFGs over conventional I-girders; and (2) to verify the adequacy of analytical models by comparing experimental and analytical results. The experimental results demonstrate the improved lateral torsional buckling capacity of CFTFGs, and their capability to carry factored design loads under construction conditions and in the final constructed condition. The comparison between experimental and analytical results shows the adequacy of simple analytical models for CFTFGs.

Stability Bracing Requirements for Steel Bridge Girders with Skewed Supports

Cross frames and diaphragms are critical elements for the stability of I-shaped steel bridge girders during construction. The AASHTO specifications are relatively vague with regards to the stability design requirements of the braces. Spacing limits that have been used in past AASHTO specifications have been removed from the Load and Resistance Factor Design Specification, which instead requires the bracing to be designed by a rational analysis. Whereas the AASHTO specification does not define what constitutes a rational analysis, stability bracing systems must possess adequate stiffness and strength. The commercially available software packages that are typically used in bridge design generally do not have the capabilities to determine the adequacy of the bracing from a stability perspective. This paper outlines the stability bracing requirements for bridges with normal and skewed supports. The effects of support skew on the stiffness and strength requirements for stability bracing are addressed. Solutions that are available for systems with normal supports were modified to account for the effects of the support skew angle. Two orientations of the intermediate bracing were considered: parallel to the skew angles and perpendicular to the longitudinal girder axis. The solutions are presented and compared with finite-element results. The design solutions have good agreement with the finite-element solutions.