Performance Of Steel Structures Research Articles

Enhancement of an intumescent fire shield paint from the nanotube rutile mineral for the fire performance of steel structures

Building and construction fire safety is an important issue for the protection of people and property. Research investigates nano-rutile minerals' synergistic role in intumescent fire shield paint (IFSP). A synergistic ingredient was introduced to intumescent fire shield paint to evaluate its impact on char morphology, fire protection test, fire propagation test, and compare it with current market products. A hydrothermal process was used to create a rutile mineral, with various techniques used to describe its structure, size, and composition. Intumescent char was found in a furnace using FESEM and X-ray fluorescence. The results showed that rutile minerals contain a rutile phase and a nanotube structure. The surface of the sample IFSP A's char showed layer and foam structures with homogenous voids during a fire test, indicating a high porosity structure. Large holes and recurring gaps were observed in the char of the IFSP B, C, and D. Sample IFSP A took more time at the structural critical temperature (about 550 o C) than other intumescent fire shield paint samples, making it a barrier layer that effectively shields the metal substrate from heat. The intumescent char residue had the highest C/O ratio of 0.57, indicating the best char yield degree and anti-oxidation abilities. The IFSP A had a phosphorous content of 36.2%, which could combine with phosphorus and TiO2 to form a ceramic barrier. The increased TiO2 in IFSP A suggests that char layers with TiO2 may still contain strong ceramic structures and function as effective thermal protection layers.

Advanced seismic resilient performance of steel MRF equipped with viscoelastic friction dampers

This paper demonstrates the enhanced resilience performance of steel structures with viscoelastic friction dampers (VEFDs) based on numerical simulations of building responses. Velocity-dependent dampers, which are widely used to increase seismic resilience, may increase the axial force of the column under strong earthquake conditions because the generated force depends on the interstory velocity. This often leads to plastic hinges being placed on the columns of the structure, which can lead to structural collapse via weak-layer failure. In addition, while viscoelastic dampers are effective in reducing story drift, peak acceleration, and peak velocity, the proposed hybrid VEFD offers the additional benefit of reducing base shear via the friction damper. Simulation results for 10- and 20-story buildings with the novel VEFDs show that the proposed dampers can control drift and plastic deformation in structural members. Nonlinear dynamic analysis of 20 far-fault seismic ground motion records conducted using OpenSees also reveals lower peak absolute floor acceleration and velocity. Overall, the results suggest that the proposed VEFD has excellent potential for use in the performance-based seismic design of structures because it can reduce both structural and nonstructural damage. The results verify the damper's effectiveness in controlling story drift without a significant increase in the base shear. Collapse probability assessment also demonstrates the collapse resistance of moment-resisting frames when used in conjunction with VEFDs.

Laser shock peening for enhanced fatigue resistance in steel structures: Insights from Q960 steel study

Fatigue damage of steel structures is often likened to the “cancer” of structural engineering. Fatigue failure, characterized by the absence of apparent signs before occurrence, usually leads to significant losses. To investigate the potential of laser shock peening (LSP) as an effective method for improving the fatigue performance of steel structures, square plates and compact tension (CT) specimens made of Q960 structural steel were designed. The surface integrity, fatigue crack growth (FCG) performance, microstructural grain size, and fracture morphology of specimens were compared at different laser shock parameters. The results show that LSP implanted a high level of beneficial residual compressive stress in a mild way, and no obvious surface defects were introduced. A noticeable retardation effect was found in the FCG of LSPed specimens, and this effect becomes more pronounced with the increase of laser pulse energy. Compressive residual stress is a more dominant factor in enhancing fatigue performance compared to grain refinement for the small-grained metals studied. LSP can effectively reduce the FCG rate of Q960 high-strength steel, showing promising application prospects in strengthening the fatigue hazard zone of steel structures.

Steel ribbed dome structural performance with different node connections and bracing system

The conventional design of steel structure objects relies on a first-order elastic analysis, where the entire object is treated as a set of individual structural elements requiring time-consuming, semi-empirical design calculations. Such an approach leads to inefficient design time and excessive material consumption and may additionally result in designing on the verge of structural safety. The AEC sector's technological and digitization advancement process forces designers to use advanced design methods. Hence, it is necessary to indicate the benefits of using effective optimization. The paper presents a comparative analysis of steel domes using two design approaches: traditional first-order analysis and an advanced second-order analysis. The latter method considers the influence of structural deformation on the magnitude of internal forces. Eight models were developed, varying in terms of the connection's stiffness. The work results identify the differences between the two selected design approaches and present opportunities for further structural performance of steel structures.

Study on the Anti-Progressive Collapse Behavior of Steel Frame Structures under Close-Range Blast Loading

The steel frame structure plays an important role in strategic deployments and is widely used in heavy machinery, metallurgy, military, and other important industries. To study the impact of explosive loads on the anti-progressive collapse performance of steel structures, this paper proposes to establish the vulnerability characteristics of steel frame structures and provides a method for calculating vulnerability characterization indicators. A finite element model is used to analyze the dynamic response of steel frame structures under the action of close-range explosive loads, and factors influencing the anti-progressive collapse of steel frame structures are proposed, including the number of stories and diagonal bracing. A comparison is made between the various column types of steel structures under explosive loads, such as corner columns, long-edge middle columns, short-edge middle columns, inner columns, also in various coupling conditions. The results show that the progressive collapse of steel frame structures is greatly influenced by the position of the explosion and less affected by the amount of explosive material. The simultaneous failure of corner columns and long-edge middle columns is more likely to cause overall structural failure. The addition of diagonal bracing significantly improves the anti-progressive collapse ability and prevents the lateral displacement of steel frame structures; increasing the number of stories provides more alternative load transfer paths for steel frame structures, thereby preventing their collapse.

Effect of U-Shaped Metallic Dampers on the Seismic Performance of Steel Structures based on Endurance-Time Analysis

Seismic performance of steel moment-resisting frames is investigated through the incorporation of U-shaped metallic dampers. The primary objective is to assess the effectiveness of these dampers in mitigating seismic responses by utilizing various analysis techniques. Two representative structural configurations (5 and 10-story) are studied in both damped and undamped states to reveal the impact of dampers on seismic response reduction. The study utilizes the endurance time analysis (ETA) method, known for its efficiency in evaluating structural seismic performance. To validate the analysis results, a benchmark comparison is made through nonlinear time history analysis (NTHA). Incremental dynamic analysis (IDA) is also conducted to assess structures’ intensity measures with respect to their damage intensity index. The findings demonstrate that U-shaped metallic dampers substantially reduce inter-story drift and story shear forces. Importantly, a close alignment between the results obtained from ETA and NTHA underscores the reliability of the former in assessing seismic performance with supplemental damping devices.

Enhancing Structural Resilience: Exploring the Novel Sleeve Method for Steel T-Stub Connections

A new sleeve device has been introduced with the aim of enhancing the performance of steel structures under extreme loading conditions. Previous research has primarily focused on numerical simulations of this sleeve's application, emphasizing the need for further investigation to validate its effectiveness. This research paper presents a numerical analysis that explores how the sleeve device influences the deformation capacity and strength of a bolt up to the point of failure. The study involved the use of a T-stub connection with multiple sleeves, each featuring different geometric parameters. To assess the impact on strength and deformation capacity, a comparison was drawn between these findings and the behavior of a T-stub bolted connection without using the sleeve. In addition, Finite Element (FE) models were employed for additional parametric studies. The test outcomes demonstrated a substantial increase in the deformability of the bolted connection when utilizing the sleeve device, all the while preserving the strength and initial stiffness of the bolts. This proposed sleeve method in the study significantly enhances the connection's capacity by delaying bolt failure.

Seismic performance of steel structures with seesaw-twisting system using cylindrical steel slit damper

A previous study proposed a seesaw-twisting system (STS) that works in conjunction with a cylindrical steel slit damper (CSSD) by utilizing the torsion of the seesaw member. This study investigated the seismic performance of an STS using a three-story steel moment frame as a prototype building. The seismic response analyses focusing on a typical STS configuration were first performed. The peak inter story drift angles were examined under variations in the beam section, system stiffness and strength, and system specifications. An important characteristic of an STS is its ability to enable the use of long steel rods for bracing between the seesaw member and frame connections spanning multiple stories. Thus, additional frames with four distinct STS configurations were analyzed to examine the peak story drift angles and plastic hinge formation. The effect of the amplification factor on the seismic response of the frame with diverse configurations was discussed. The results showed that the STS with the CSSD efficiently reduced peak story drifts.

Seismic performance and hysteretic model of corroded steel frame columns in offshore atmospheric environment

Previous studies show that the offshore atmospheric environment corrosion gradually reduces the physical and mechanical properties of steel and eventually deteriorate the seismic performance of steel structures. This paper presents a comprehensive study on the seismic performance of corroded steel frame columns in offshore atmospheric environment. Artificial climate accelerated corrosion tests and cyclic loading tests were carried out on six steel frame columns. The effects of corrosion level and axial compression ratio on the failure mechanism and seismic performance of the columns were investigated in details. The test results indicate that with an increase in corrosion level or axial compression ratio, the displacements associated with plate local buckling, plastic hinge formation and final failure tend to reduce gradually. The bending capacity, ductility and energy dissipation capacity of columns also significantly decrease, and the strength and stiffness degradation effect intensify. Furthermore, a moment-rotation hysteretic model in plastic hinge zone for corroded steel frame columns, considering the cyclic deterioration in strength and stiffness, was established by introducing a two-parameter seismic damage model. The predicted moment-rotation curves and energy dissipations coincided well with the experimental results, verifying the rationality and applicability of the proposed hysteretic model. The research results provide theoretical support for elastic-plastic time history analysis and seismic risk assessment of existing steel frame structures in offshore atmospheric environment.

Experimental investigation of blast resistance of steel structures with different elastomeric coatings subjected to underwater explosive loading

Elastomeric material is used as blast-resistant structure because of its good mechanical properties.A series of underwater near-field explosive tests at different standoff distances were conducted to investigate the anti-explosion performance of steel structures covered with rubber and polyurea coatings. The experimental results demonstrated that both rubber and polyurea could enhance the blast resistance of test plates, and the polyurea coating performed better in reducing the deformation of steel plate and damage of steel structure. Compared with rubber, the polyurea has excellent mechanisms of energy absorption and dissipation, its mechanical behavior and molecular structure of elastomeric material determines the different ways of energy absorption and dissipation.

Assessing seismic performance of code-compliant steel special moment frames using ASCE 41-17

ASCE 41 standard, increasingly used by practitioners, is a desirable tool to evaluate the seismic performance of different types of structures according to the Performance-Based Earthquake Engineering framework. The latest edition of this standard (ASCE 41-17) has undergone significant changes with respect to its previous versions, which could substantially affect the results of structural performance evaluation. Within this context, the present study performs a comprehensive quantitative investigation of the seismic performance of steel structures based on the component-level Tier 3 systematic evaluation procedure of ASCE 41-17, using both nonlinear static (conventional and enhanced pushover analyses) and dynamic analyses. The evaluation is conducted on six ASCE 7 code-compliant steel special moment frames considering different heights (i.e., 6, 12, and 18 stories) and two versions of the seismic design code (i.e., ASCE 7-10 and -16). The results of the nonlinear dynamic procedure demonstrate that both the ASCE 7-10 and -16 designed buildings satisfy the acceptance criteria of ASCE 41-17. It is also shown that the linear dynamic procedure recommended by ASCE 41-17 to supplement the results of the nonlinear static procedure for buildings with significant higher modes effect cannot provide an accurate estimation of the structural performance compared to enhanced pushover procedures. Additionally, the comparison of the structural performance evaluation between the ASCE 41-13 and -17 indicated that the previous edition of this code (ASCE 41-13) is overly conservative for columns compared to ASCE 41-17. Finally, the applicability of using the modeling parameters recommended by ASCE 41 for simulating the elements’ behavior in case of the lack of sufficient available experimental data is demonstrated.

Norm and interpolation based absolute stress evaluation in steel members using the Lcr wave

The uniaxial absolute stress in steel members is a vital indicator for evaluating the performance of steel structures. Non-destructive ultrasonic detection is widely applied in the absolute stress measurement of steel members with the advantages of easy implementation, no limits on materials and high precision. The acquisition algorithm of time-of-flight (TOF), the sampling rate of ultrasonic signal and the processing of outliers determine the accuracy of the stress measurement. In this study, we proposed a norm and interpolation based algorithm for absolute stress measurement using the longitudinal critically refracted (Lcr) waves, which improves the accuracy and velocity of the absolute stress measurement. Firstly, the norm was designed to obtain the TOF of the ultrasonic signal. When only the Lcr wave arose in the ultrasonic signal, the two-norm similarity algorithm was found to be consistent with the cross-correlation-based algorithm and the corresponding theoretical expressions were derived. With the non-Lcr wave in the ultrasonic echo, the two-norm similarity algorithm has stronger anti-interference ability. Secondly, the pchipslopes, spline and linear interpolation algorithms were introduced via which the TOF of ultrasound with low sampling rate reaches the same accuracy as that of high sampling rate signal. Finally, a special class of outliers in TOF was explored, and a threshold based on the number of shift points and the stress feature was proposed to calibrate these outliers to normal values. Experiments demonstrate the proposed algorithm improves the accuracy and velocity of uniaxial absolute stress measurement in structural steel members.

Performance Assessment of Hybrid Steel Frames under Near-field Seismic Excitations

Assessment of the seismic performance of steel structures is topical research for a variety of earthquakes. Moment-resisting rigid steel frames are generally designed and used for high seismic zones. However, the famous Northridge in 1994 and Kobe in 1995 earthquakes exposed the shortcomings of moment frames. During these events, the beam-column connections of rigid moment frames were severely damaged. Since then, an alternative of welded connections called bolted or semi-rigid connections is considered for designing or retrofitting of steel moment frames. From the last few years, the semi-rigid connections combined with rigid connections, termed as hybrid or dual frames have become widely popular for earthquake designers and engineers due to enhanced ductility and reduced cost of construction. Earlier research work was focused on far-field (FF) earthquakes, whereas, the near-field (NF) earthquakes are crucial for civil engineering structures. In this paper, an extensive numerical study is carried on rigid and hybrid steel moment frames for NF and FF earthquakes. For this purpose, a ten-story rigid steel frame is analyzed and designed for seismic requirements as per Indian Standards. The rigid connections of frames are replaced by semi-rigid connections with a moderate degree of semi-rigidity. The six different patterns (locations of semi-rigid connections) of hybrid frames are considered here to compare the seismic performance of hybrid frames under near field earthquakes. The nonlinear response-history analyses are executed using the SAP2000 software at two scaled PGAs defined as low (i.e., 0.2g) and high (0.5g) level. An ensemble of three time-histories, each for both types of earthquakes are considered for the numerical simulation. Response quantities of interest, namely, the maximum value of base shear, story displacement, inter-story drift ratio, the total number of plastic hinges, and the square root of the sum of squares of maximum plastic hinge rotations are considered for the decision of a most appropriate pattern for hybrid frames. The results of the numerical study indicate that the response behavior for the NF earthquakes is distinctly different both in nature and magnitude. It is observed that the seismic demands under the NF earthquakes are substantially more as compared to those obtained for FF earthquakes for all cases of hybrid frames. Further, it is also found that the pattern and number of semi-rigid connections in the hybrid frame have a vital role in seismic performance.

Experimental investigation into mechanical properties of Q345 steel after fire

The fire hazard has been considered one of the prominent risks for steel structures. After cooling from high temperatures, the mechanical properties of steel can be changed, which has a great influence on structural safety. Therefore, assessing the performance of steel structures after a fire necessitates a profound understanding of the post-fire mechanical properties of steel. Q345 steel is the most commonly used steel grade in China. In this research, an experimental study was undertaken to investigate the post-fire mechanical properties of Q345 steel. Coupon tests of base metal and weld were carried out with the maximum temperatures elevated to 1000 °C. Two cooling methods were adopted, including cooling in air and water. Post-fire performance was obtained and compared, such as the appearance, stress-strain curve, elastic modulus, yield strength, ultimate strength, percent elongation and percent reduction of area. It was found that for base metal, when the temperatures exceeded 600 °C, cooling in water promoted the strength notably but reduced the ductility significantly, while cooling in air increased the ductility. Moreover, the ultimate strength of base metal cooling in water was much higher than that of weld with temperatures above 800 °C, and the deterioration of plastic deformation ability of weld was more severe than in the base metal. Based on the results, a set of predictive formulas is proposed for the variation factors of the post-fire mechanical properties for the Q345 base metal as well as for the weld, helping this way the engineers in evaluating and renovating fire-damaged steel structures.

Behavior of Earthquake Damage Steel Structures in Fire

Fire following an earthquake (FFE) has become a major threat for building, particularly in seismic areas. Many FFE events have caused a high level of damage and casualties. On the other hand, current design codes do not support a specific loading case for FFE. Moreover, the modern design philosophy for seismic design allows a certain level of damage that may affect the structure's vulnerability during a post-earthquake fire. Many previous studies have investigated the structural behavior of the building under FFE. This study is intended to showcase, theoretically and practically, the numerical analysis methods used in previous studies. The main objective is to improve the understanding of the performance of steel structures under a post-earthquake fire. A brief historical review of the numerical analysis methods is presented. It is observed that there are four stages of analyses adopted in the previous studies, which are structure system, earthquake analysis, fire analysis, and evaluation. However, different concepts and methods have been used in every stage. This study discusses the advantages and disadvantages of the design concept and the numerical analysis method. It was found that the key aspect of fire following an earthquake analysis is interpreting earthquake damage as an initial condition for the subsequent fire action. The 3D model is required since the composite slabs have a significant role in the frame's survival through tensile membrane action. Furthermore, several parametric fires must be considered to simulate a fire event after an earthquake.

Test on post-fire residual mechanical properties of high strength Q690 steel considering tensile stress in fire

As a steel building may not fail in a fire scenario, the residual mechanical properties of steel after fire exposure are essential in evaluating the post-fire performance of the steel structure. However, the current experimental research regarding the post-fire mechanical properties neglects the stress in steel during the heating and cooling phases, which violates the fact that a steel structure still carries load during a fire hazard. In order to quantitatively assess the influence of stress level in steel structures on post-fire residual mechanical properties of high strength steels, a series of tensile tests was carried out on a typical high strength Q690 steel specimen exposed to elevated temperatures under three stress ratios, namely 0.30, 0.55 and 0.80. During the heating and cooling phases, constant stress was applied on the specimen to simulate the possible stress in steel structures in fire hazards. After cooling, tensile tests were carried out to attain the post-fire stress-strain curves of Q690 steel, and accordingly determine the residual yield strength, ultimate strength and elastic modulus of Q690 steel with different temperature exposures and stress levels. The test results show that the tension stress in steel during heating and cooling can improve the post-fire yield strength and ultimate strength of Q690 steel with the maximum 8% when the exposed temperature is lower than 700 °C, and the improvement increases as the stress level increases. However, the tension stress has adverse effect on the post-fire strengths of Q690 steel when the exposed temperature reaches 800 °C. If the exposed temperature is below 700 °C, it is safe to take the original strengths of Q690 steel to evaluate the post-fire performance of Q690 steel structures. However, the stress effect on the residual strengths should be considered if the exposed temperature reaches 800 °C to avoid unconservative evaluation. The tension stress in steel has no significant influence on residual elastic modulus of Q690 steel. By comparing the obtained test data with other post-fire tests on similar steels, it is found that the post-fire residual mechanical properties of steels are different even if those steels have the same nominal yield strength. The maximum 40% dispersion for residual yield strength and 50% dispersion for ultimate strength are found when the exposed temperature surpasses 600 °C due to rolling, quenching and tempering for high strength steels.

Effect of pre-fatigue damage on static and hysteretic behavior of Q355 steel

The mechanical behavior and low cycle fatigue properties of Q355B structural steel subjected to different levels of pre-fatigue damage were investigated in the present study. Monotonic tensile and low cycle hysteresis loading tests were carried on Q355B steel coupons with pre-fatigue damage to investigate its influence on the mechanical properties of Q355B steel. A reliable relationship between the mechanical behavior and the pre-fatigue damage under cyclic loading was subsequently established. The findings from the present research provide a valuable reference for the accurate assessment of the mechanical performance of steel structures after varying degrees of pre-fatigue damage.

Numerical Investigation of the Post-Fire Performance of Steel Columns

Research on the seismic performance of steel structures has led to the development of improved structures, which minimize structural and non-structural damage and can be reused immediately after an earthquake. Moreover, significant advances have been made for predicting the response of steel members, connections, and structural systems exposed to fire. Nevertheless, the research on the reuse of steel structures after a fire event is limited. A steel structure designed according to the current seismic codes can survive a fire without significant structural damage and may be repaired and reused. Therefore, it is of great importance to study whether the reuse of steel structures after a fire is safe in high seismicity areas. This paper investigates the seismic performance of steel columns that are pre-damaged due to fire. For this purpose, sophisticated finite element models have been developed and validated against experimental data. It was concluded that the models accurately predict the behaviour of beams-columns at elevated temperatures. First, the behaviour of the columns was studied using simplified boundary conditions; the surrounding structure was not included in the numerical model. Thermal-structural analyses were performed to determine the structural damage induced by the fire. Subsequently, the cyclic performance of the columns was investigated, considering both the residual post-fire deformations and the proper material properties. Aiming to obtain more realistic results, the complicated interaction between the heated columns and the surrounding structure was considered in the modelling. For this reason, the fire behaviour of a seismic resistant frame was simulated. Then, the behaviour of fire-damaged columns under cyclic loading was assessed. The analysis of the results demonstrates the effect of the post-fire damage on the cyclic behaviour of columns.

The Effect of Atmospheric Corrosion on Steel Structures: A State-of-the-Art and Case-Study

Atmospheric corrosion can seriously affect the performance of steel structures over long periods of time; thus, it is essential to evaluate the rate of corrosion and subsequent modification of dynamic properties of a structure over different time periods. Standards and codes represent the general guidelines and suggest general protection techniques to prevent structures from corrosion damage. The available models in the literature propose the thickness reduction method that accounts for the exposure time of structures in corrosive environments. The purpose of this study is to review the existing corrosion models in the literature and report as well as compare their effectiveness in low (C2 level), medium (C3 level) and high (C4 level) corrosivity class in accordance with the ISO standard. Furthermore, the influence of corrosion loss during the lifetime of a structure is studied through a realistic case study model using FEM (finite element method) in both linear and nonlinear regions. The results showed that the corrosion can considerably affect the dynamic characteristics of the structure. For instance, the vibration period rose up to 15% for the C4 class and 100-year lifespan. Additionally, the corroded structure presented higher acceleration and drift demand, and the base reaction forces were reduced up to 60% for the same class and time period.

Effect of surface preparation technique on fatigue performance of steel structures repaired with self-stressing SMA/CFRP patch

An experimental program was conducted to evaluate the effect of surface preparation on the effectiveness of a shape-memory alloy / carbon-fiber reinforced polymer (SMA/CFRP) self-stressing patch for repair and strengthening of fatigue-sensitive steel elements. Steel surfaces were prepared through grit blasting and power tool cleaning. The fatigue lives of control and repaired specimens were measured to quantify the improvement provided by the patch under Mode-I loading. Fatigue crack growth curves were developed using a beach marking technique to track the evolution of crack growth. Digital-image correlation techniques were implemented in selected cases to study the debonding of the patch from the steel for different configurations and load levels. The fatigue performance of repaired specimens is investigated in terms of failure modes, fatigue lives, crack growth curves, and strain contours. This discussion is informed by the results of surface characterization tests performed on grit-blasted and power-tool-cleaned surfaces. It was found that grit-blasted repaired specimens exhibit approximately three-times the fatigue life improvement experienced by their power-tool-cleaned counterparts.