Steel Frame Buildings Research Articles

Improving the robustness of steel frame structures under localised fire conditions

PurposeThe robustness of building structures in a fire has recently drawn wide attention. This study presents the progressive collapse analysis of steel frame building structures under localised fire. The main objective of this study is to propose methods to enhance the structural collapse resistance of such structures in fire.Design/methodology/approachA modelling method was developed and validated against both experimental and analytical studies. Then, a series of robustness analyses were performed to investigate the interaction among the members and the pattern of load distribution within the structures. These analyses show that lateral resistance and load redistribution have a vital role in the robustness of the building. Thus, two approaches have been adopted to enhance the robustness of the focused steel frame during a fire.FindingsIt is found that increased size of floor beams and vertical bracing systems are effective measures in preventing whole structure collapse. The larger beam section is able to prevent catenary action so that the load in the failed columns can safely transfer to the adjacent columns without buckling. On the other hand, the bracing system improves the lateral resistance that can accommodate the lateral force when catenary action occurs in the beam.Originality/valuePrevious studies have focused on the collapse mechanism of steel frame structures. However, the parameters affecting the structural robustness in a fire have not yet been explored. To address this gap, this study adopted numerical modelling to undertake parametric studies to identify effective methods to improve the robustness of such structures under fire conditions.

Vibration transmissions and predictions within low-rise buildings above throat area in the metro depot

Train-induced feelable vibrations can bring side effects to people living or working in the building, as well as to operation of precise equipment. As massive construction of over-track buildings above metro depots prevails in megacities, impacts from train-induced feelable vibration take more concern. Four standard-designed 4-story steel-framed offices above the throat area in the Qianhai metro depot in Shenzhen, China, are studied in this research. The field measurements were conducted to investigate the influences of track alignment and track location in the throat area on vibration responses of over-track buildings. Detailed vibration analyses using the finite element method have been conducted. Train-induced floor vibration assessments on human comfort are carried out based on a total of 54 train pass-bys operated in the morning and evening and on different tracks. It can be found that the track alignment primarily affected the higher frequency components of train-induced vibrations, where curved trackinduced vibrations have larger amplitudes. The variance of train-induced building vibrations among pass-bys on different track locations was reduced compared with that of ground vibrations because of the averaging effects caused by multiple transmitting paths within the massive platform and stiff transfer structures. Train-induced acceleration levels at mid-floor can be 20–25 dB larger than those near columns at floor resonance frequencies which are dependent on the structural design. This research gives a comprehensive insight into train-induced vibrations within low-rise steel-framed buildings above the throat area in the metro depot, which is a valuable reference for assessments before the construction of future similar over-track communities.

Effects of demand parameters in the performance-based multi-objective optimum design of steel moment frame buildings

This paper investigates the effects of various demand parameters involved in the optimal performance-based design of steel moment frame buildings. These parameters include the peak values of story drift ratio, floor velocity, floor acceleration, and residual drift ratio. The performance-based design is performed to minimize two conflicting objectives, including the initial construction cost and the expected annual repair cost of the building under the design constraints. FEMA P-58 is utilized as a comprehensive and popular methodology for seismic risk assessment and building loss estimation in this paper. It evaluates the building performance in a probabilistic manner in terms of several metrics such as repair cost, repair time, carbon emissions, embodied energy, injuries, and fatalities. The Monte Carlo analysis is used to consider various uncertainties affecting seismic performance. A set of three steel moment-resisting frame (MRF) buildings representative of low-to mid-rise frames are selected as a case study in this research. The results of this study indicate that the story drift ratio has a major role in the performance-based optimal design of steel MRFs. Accordingly, despite increasing the two parameters of floor acceleration and floor velocity due to increasing the initial cost of structural moment frames, the annual repair cost of the building decreases when the story drift ratio decreases.

Effect of Non-Structural Components on the Dynamic Response of Steel-Framed Floors: Tests Before and After Component Installations

The effect of partition walls and non-structural elements on the dynamic response of floors is still not well understood, and there is a need for vibration testing of floors at various stages of construction. The best way to shed some light on the effect of non-structural components is to test additional floors (preferably the same floor) before and after the installation of non-structural elements and compare the dynamic properties. For that purpose, the authors conducted vibration testing on a building floor under construction at various stages of fit-out to quantify the effects of various non-structural elements on the vibration response. An elevated floor of a steel-framed building in the Southeastern United States was tested: the first test was performed for the bare slab conditions with minimal non-structural elements, while the second test was conducted after the installation of non-structural components and in the presence of various construction materials spread over the test floor. The modal tests were conducted by applying measured dynamic forces using an electrodynamic shaker while accelerations were measured at critical locations on the slab. The measurements were post-processed to determine the frequency response functions, which provided general information on the dynamic response. The selection of the test points and excitation functions were primarily to extract maximum data regarding the performance of non-structural elements rather than as part of a standard vibration serviceability assessment of the floor structure. The modal tests were repeated after the installation of non-structural components, electrical and mechanical ductwork, to determine their effect on the vibration characteristics of the floor. The resulting frequency response functions were compared for each condition, and finite element models were created to represent each test condition. As a result, the installation of non-structural components was observed to influence the dynamic response of the floor. Combined with the other test data in the literature, the results of the experimental testing presented in this paper might lead to more effective modeling techniques and provide guidance as to their inclusion into analytical models.

Design of electromagnetic induction calculation and auxiliary calculation software under UHV transmission line

With the development of 1000 kV UHV transmission technology and the shortage of line corridor resources, UHV will inevitably cross the building area. Although many scholars had studied the power frequency electromagnetic field under UHV AC transmission line, it is very difficult to accurately calculate the electric field strength and induced voltage, which cannot be applied in engineering. At present, there is no relevant literature to study the problem of induced electricity in buildings with a large number of steel frame structures under the line and the estimation method of induced electricity in buildings. By summarizing and analyzing the simulation data, the estimation method of induced voltage and induced current density of steel frame buildings under UHV lines was proposed. An auxiliary calculation system was developed. The calculated values of the software were compared with the measured values, which accuracy of voltage and current can reach 91.5% and 92.7%, and fully meet the engineering needs.

Sparse Bayesian learning for damage identification using nonlinear models: Application to weld fractures of steel‐frame buildings

Sparse Bayesian learning (SBL) is a well-established technique for tackling supervised learning problems, while taking advantage of the prior knowledge that the expected solution is sparse. Based on the premise that initial damage of a structure appears only in a limited number of locations, SBL has been explored for identifying structural damage, showing promising results. Existing SBL methods for structural damage identification use measurements related to modal properties and are thus limited to linear models. In this paper, we present a methodology that allows for application of SBL in nonlinear models, using time history measurements. We develop a two-step optimization algorithm in which the most probable values of the structural model parameters and the hyperparameters are iteratively obtained. An equivalent, single-objective, minimization problem that results in the most probable model parameter values is also derived. We consider the example problem of identifying damage in the form of weld fractures in a 15-story moment-resisting steel-frame building, using a nonlinear finite-element model and simulated acceleration data. Fiber elements and a bilinear material model are used to account for the change in local stiffness when cracks at the welds are subjected to tension, and the model parameters characterize the loss of stiffness as the cracks open under tension. The damage identification results demonstrate the effectiveness and robustness of the proposed methodology in identifying the existence, location, and severity of damage for a variety of different damage scenarios and levels of model and measurement error.

Development of an Analytical Model to Determine the Heat Fluxes to a Structural Element Due to a Travelling Fire

The term “travelling fire” is used to label fires which burn locally and move across the floor over a period of time in large compartments. Through experimental and numerical campaigns and while observing the tragic travelling fire events, it became clear that such fires imply a transient heating of the surrounding structure. The necessity to better characterize the thermal impact generated on the structure by a travelling fire motivated the development of an analytical model allowing to capture, in a simple manner, the multidimensional transient heating of a structure considering the effect of the ventilation. This paper first presents the basic assumptions of a new analytical model which is based on the virtual solid flame concept; a comparison of the steel temperatures measured during a travelling fire test in a steel-framed building with the ones obtained analytically is then presented. The limitations inherent to the analyticity of the model are also discussed. This paper suggests that the developed analytical model can allow for both an acceptable representation of the travelling fire in terms of fire spread and steel temperatures while not being computationally demanding, making it potentially desirable for pre-design.

Generalised Component Method-based finite element analysis of steel frames

The design-by-analysis approach lays the foundation for the next generation of structural design standards in which the strength and structural safety check are performed in a single step at system level, without recourse to a structural standard for individual member checks. However, to date, no attempt has been made towards considering the failure of joints in the structural analysis, without which the complete set of limit states cannot be accurately predicted. This paper presents a new analysis approach that incorporates macro-element joint models based on the Generalised Component Method in the FE analysis of steel frame buildings. The new analysis approach is termed Generalised Component Method-based finite-element (GCM-FE) analysis. The fundamental aspects and principles of the GCM-FE analysis approach are established in this paper, including the framework of GCM-FE analysis, the constitutive models for the connection components and the implementation of GCM-FE analysis in commercial numerical software including an automatic modelling technique. The GCM-FE joint modelling method is first validated against the experimental results of three steel beam-to-column connection types, including the bolted moment end-plate connection, top-and-seat angle connection and web angle connection. GCM-FE analysis is subsequently performed on a two-storey four-bay irregular steel frame, showing apparent advantages over the traditional analysis methods which adopt simplified joint models. The GCM-FE analysis not only provides the ultimate resistance and failure mode of the frame, but also accurately predicts the load-redistribution process inside the connections and the resultant effect on the structural framework.

Image Motion Extraction of Structures Using Computer Vision Techniques: A Comparative Study.

Vibrational measurements play an important role for structural health monitoring, e.g., modal extraction and damage diagnosis. Moreover, conditions of civil structures can be mostly assessed by displacement responses. However, installing displacement transducers between the ground and floors in real-world buildings is unrealistic due to lack of reference points and structural scales and complexity. Alternatively, structural displacements can be acquired using computer vision-based motion extraction techniques. These extracted motions not only provide vibrational responses but are also useful for identifying the modal properties. In this study, three methods, including the optical flow with the Lucas–Kanade method, the digital image correlation (DIC) with bilinear interpolation, and the in-plane phase-based motion magnification using the Riesz pyramid, are introduced and experimentally verified using a four-story steel-frame building with a commercially available camera. First, the three displacement acquiring methods are introduced in detail. Next, the displacements are experimentally obtained from these methods and compared to those sensed from linear variable displacement transducers. Moreover, these displacement responses are converted into modal properties by system identification. As seen in the experimental results, the DIC method has the lowest average root mean squared error (RMSE) of 1.2371 mm among these three methods. Although the phase-based motion magnification method has a larger RMSE of 1.4132 mm due to variations in edge detection, this method is capable of providing full-field mode shapes over the building.

New composite flooring system for the circular economy

Circular economy is an economic system aimed at minimizing wastes and making the most of the current resources. This regenerative approach contrasts with the traditional linear economy, which has been adopted by the construction industry. Developing new construction technologies for sustainable built environment is a top priority for the construction industry throughout the world. Much of the environmental impact from the construction industry is associated with the consumption of resources and generation of waste. The construction industry in Europe consumes over 70,000 million tonnes of materials each year and generates over 250 million tonnes of waste. Composite flooring formed by connecting the concrete slabs to the supporting steel beams has been widely used for many years and is well established as one of the most efficient floor systems in multi-storey steel frame building structures. However, shear connectors are welded through the steel decking to the steel beams and cast into the concrete; this made deconstruction and reuse of these components almost impossible. A new composite flooring system which allows for the reuse of the steel beams and composite floor slabs is developed and tested to assess its potential and suitability for reuse. This paper presents the results of a series of full-scale beam tests and demonstrates the reusability of this new form of composite flooring systems. Simplified hand calculations are also provided and compared against beam tests.

The influence of loading rate on the ultimate capacity of bolted T-stubs at ambient and high temperature

In case of accidental actions, the robustness of multi-storey steel frame buildings depends to a large extent to the performance of the beam-to-column joints. For an extreme scenario that involves a column loss under fire, the dynamic process can induce high strain rates and therefore needs to be considered when evaluating the resistance and ductility of the beam-to-column connections. End plate bolted connections are widely used in the steel framed constructions. The simple macro-component through which the response of such a connection is assessed, consists in the T-stub model included in EN1993-1-8.The paper presents the results of an experimental program on T-stubs subjected to normal and high temperatures, in both quasi-static and high loading rate conditions. While under normal temperature the response of the T-stubs are not significantly influenced by the strain rate, at high temperatures the strain rate determines a change in the failure mode and in the ultimate resistance and deformation. The experimental study highlights the necessity of assessing the strength reduction factors of bolts function of both temperature and strain rate, a critical information in the progressive collapse assessment of structures under fire, in order to obtain realistic results.

Structural Fire Analysis of One‐storey Steel‐framed Buildings with Steel Claddings

AbstractTraditionally the structural stability of steel building frames is ensured by frame action or bracing elements. Recent European research projects have demonstrated that significant cost savings can be achieved, if cladding panels forming the building envelope are used to provide stability. The purpose of the paper is to investigate the possible stabilization effect of steel structures by steel claddings in fire, without additional wind bracings using Finite Element Method. The Finite Element analyses for full‐scale steel‐framed buildings with steel claddings under fires are still challenging due to large number of elements in the steel claddings. In this paper, the equivalent orthotropic shell element is used to model the trapezoidal roof sheeting, and composite shell element with soft core is used to model the sandwich panel in the cool compartment. Due to the delamination of inner steel face in fire, the sandwich panels in the fire compartment can be either neglected or modeled with two‐layer composite shell ignoring the inner steel sheet. The comparative study is performed, and the results suggest that the difference is small and the sandwich panels in the fire compartment can be neglected. The stabilization effect of steel claddings in fire is studied by the comparison of deformation and force responses between buildings with traditional steel bracings and with steel cladding only. In case of ISO fire, the fire resistance of entire one‐storey building with steel claddings only is 22% longer than the one with traditional steel bracings.

Earthquake and Postearthquake Fire Testing of a Midrise Cold-Formed Steel-Framed Building. I: Building Response and Physical Damage

AbstractTo advance understanding of the multihazard performance of midrise cold-formed steel (CFS) construction, a unique multidisciplinary experimental program was conducted on the Large High-Perf...

Earthquake and Postearthquake Fire Testing of a Midrise Cold-Formed Steel-Framed Building. II: Shear Wall Behavior and Design Implications

AbstractComplementing a companion paper that summarizes the building global response and physical damage of a midrise cold-formed steel (CFS) framed building during an earthquake and postearthquake...

Behaviour of Multi-storeyed Steel Building with Steel Plate Shear Wall

The present study describes the analysis and design of high-rise steel building frame with and without Steel plate shear wall (SPSW). Further it is compared with moment resisting steel framed building and X-Braced steel framed building. For present work Response Spectrum Analysis is carried out for steel moment resisting frame building having G+19 storey situated in zone III. Modeling is done by using strip modeling. The analysis of steel plate shear wall and the building are carried out using software SAP2000 V15. The main parameter considered in this project is to compare the seismic performance of buildings i.e. lateral deflection. The models are analyzed by Response Spectrum analysis as per IS 1893:2002 and design has been carried out by using IS 800-2007.

Structural assessment of an existing steel frame building for adding new story by linear static analysis

The primary objective of this work is to assess the condition of an existed structural steel frame building that is already occupied by users, and to investigate the load bearing capacity of the major structural members (beams, columns) of the steel frames, so that to find out the possibility of added additional new story that can help to increase the capacity of the building. It was decided by the authorities and the building officials to add another story to accommodate an expansion to increase the occupancy capacity of the building. Structural analysis of the building frames due to original loads would be implemented and then additional story would be added, on the other hand a structural analysis would be performed due to additional story (additional loads). Linear static analysis in both cases was done and responses was evaluated by Demand to Capacity Ratios (DCR), And by a comparison the DCR for columns in both cases, it was found that the bearing capacity of columns allow to add new story safely. Furthermore, redesign of the new building would be carried out using commercial software sap2000. The building façade, such as veneers and curtain walls are not considered as structural elements therefore, not covered in this work. (The connections of joints and foundation analysis would be covered in farther considerations using another finite element program).

Flexible stop’s force determining method in a combined plate using profiled flooring

Introduction. Steel-reinforced concrete floors with profiled decking are most often used in steel frame buildings. The joint work of the floor slab and tertiary beam is ensured by shear studs. The article discusses a shear studs stress determining method from horizontal load. Studs are placed along the slab’s perimeter. The method based on the bolts’ group calculation analogy. Materials and methods. Based on the bolts group calculation design expressions were derived to determine the force in shear studs. To determine the obtained values reliability a finite element calculation was performed using the Lira-CAD software package. Different aspect ratios slabs samples were considered. The solution’s convergence was determined by various methods for a plate with 0.6 × 0.6 m dimensions with a small number of studs, after which the proposed solution convergence was studied for real dimensions of plates with a large number of flexible stops. Results. The resulting formula allows determining the stress in each flexible stop, in particular in the most loaded corner studs. The computer calculation was performed for the proposed method clarity and using possibility. The method’s use restriction was determined. In addition, the shear studs’ geometric characteristic’s definition explanations are given. Conclusions. The proposed calculation method allows to determinate any structural section’s shear stud’s stress. Therefore, it allows to choose stud’s optimal cross-section area or check its bearing capacity in the existing buildings and structures floors. Moreover, the stress value allows to determine the stud’s and a whole slab’s deformations.

Seismic behavior and damage assessment of mid-rise cold-formed steel-framed buildings with normal and reinforced beam-column joints

Seismic behavior and damage assessment of mid-rise cold-formed steel-framed buildings with normal and reinforced beam-column joints

Disproportionate collapse of steel-framed gravity buildings under travelling fires

Observations from realistic fires have revealed that a fire tends to “travel” across the floors rather than burning simultaneously for the duration. However, the collapse mechanism and mitigation measures of structures under travelling fires are still not well understood. This paper investigates the disproportionate collapse behaviour of three-dimensional steel-framed gravity buildings subjected to travelling fires. The effect of fire curves (burning rate) and fire spreading speeds on the collapse behaviour is first studied. The effectiveness of using fire protections and bracing systems in preventing collapse is examined. It is found that the duration of the heating phase has a great effect on whether a building collapses or not, and the building may collapse during the cooling phase. A “long-cool” fire curve (slow burnig rate) is more dangerous than mild (average burning rate) and “short-hot” fire curves (fast burning rate) since the former causes a higher temperature in the structure. The fire travelling speed significantly affects the failure sequence of columns, range of damage and collapse mode of structures. For the structure analysed, a slow travelling fire (e.g. 2.5 mm/s) may lead to a partial collapse mode confined around the fire-affected region, but a global collapse in a wider range may occur in a fast travelling fire (e.g. 10 mm/s). A higher level of fire protection may prevent the collapse of structures, but may also lead to collapse in the cooling phase due to the delayed increment of temperatures in the heated members. The collapse time of a protected structure under a travelling fire is longer than the fire-resistance rating of its components (up to 130 min). Application of bracing systems (horizontal, vertical or combined) can prevent collapse of structures under a slow travelling fire, but not for a fast travelling fire. It is recommended to consider the possible fire scenarios when determining the fire-resistance rating, and increase the fire-resistance rating of components to 3 h to prevent collapse under a travelling fire with a “long-cool” fire curve. The beam-to-column connections should possess a sufficient tension and compression resistance, which may be equal to 100% and 50% of the yielding capacity of beams, respectively.

Development of a GUI Based Program for Design of various Steel Connections

Steel frame buildings consist of a number of different types of structural elements. Every element must be attached properly to its neighbouring part of structure. This will involve use of various types of connections. Connections account for more than half the cost of structural steel work. Connection failure is not a ductile failure and hence it should be avoided before member failure. Large uncertainty is there in the design of connections. Connections are usually the most vulnerable part of the structure, failure of which may lead to the failure of whole structure. Thus, design of connection is an important and integral part of design of the steel structure. This MATLAB GUI program developed will be a very useful and user-friendly tool for the design of connections.