Portal Frame Research Articles

Reliability of stainless steel frames designed using the Direct Design Method in serviceability limit states

Steel structures can be consistently and efficiently designed using system-based design-by-analysis approaches such as the Direct Design Method. However, since direct design approaches lead to potentially lighter structural configurations, they can also result in larger deformations under service loads. Thus, greater attention may be required to serviceability limit states in structures designed using design-by-analysis approaches than for structures designed elastically at their ultimate limit state following current two-stage approaches, especially for materials showing highly nonlinear stress vs strain responses such as stainless steel alloys. With the aim of investigating the influence of allowing larger deformations in the ultimate limit state design of stainless steel structures, this paper presents an explicit analysis framework for assessing serviceability reliability at system level. Using this framework, the paper investigates the serviceability reliability of cold-formed stainless steel portal frames designed using the Direct Design Method for different load cases, including the gravity load and the combined gravity plus wind load combinations. The study considers six baseline frames covering the most common stainless steel families and international design frameworks (i.e., Eurocode, US and Australian frameworks), for which the reliability of vertical deflection and lateral drift serviceability limit states is investigated using advanced numerical simulations and First-Order Reliability Methods. From the comparison of the calculated average annual reliability indices and the relevant target reliabilities for the different design frameworks, it was found that the reliability of stainless steel frames appears to be adequate for the serviceability limit states investigated for the Eurocode, US and Australian frameworks.

Research on prestressed loading strut of cable supported portal frame

In this study, a novel type of loading strut device is presented, which is introduced in portal frame external prestressing reinforcement and used to constitute a cable-supported portal frame structural system. The strut device was found to be capable of elongating by rotating the middle screw and applying prestress to the steel strand in the system. In this study, the new loading strut is simulated and analyzed using the ANSYS finite element analysis software. Moreover, it is used for the reinforcement test of a practical project. During the test, the prestress load is applied through the novel strut, and the changes of strain, mid span deflection and prestress of the steel strand at the key positions before and after the reinforcement are investigated. Based on the analysis of the simulation and test results, it is found that this novel type of loading strut is simple, safe and reliable to operate, and could be employed in the cable-supported structure system without tensioning the steel strand to achieve loading.

From the archive: Strength is easy! Or the development of plastic design

To mark the 100th anniversary of The Structural Engineer, Alan Rathbone looks back at several key papers that helped advance the development of plastic design of steel portal frames.

A steel hysteretic damper for seismic design and retrofit of precast portal frames

In this paper a steel hysteretic damper is proposed which can be installed at the beam-column joint of precast concrete structures and can greatly improve the seismic performance of these structures. The damper is made of a few steel plates with reduced sections placed in parallel, which yield under in-plane bending caused by joint rotation and dissipate energy induced by seismic activity. As less attention has been paid to seismic performance evaluation and design of precast portal frames, a procedure for design and performance estimation is established based on the available theoretical formulation and is verified by comparing their results with those obtained by analysis. The efficiency of the proposed damper is investigated by retrofitting a portal frame and evaluating its seismic performance before and after retrofit. The results show that the developed damper can significantly reduce the maximum interstory drift ratio and prevent the global collapse of the structure, which is of particular interest in practice. The hysteretic behavior and the energy dissipation capability of the frame are compared before and after the retrofit. It is observed that most of the seismic energy is dissipated by the dampers installed in the retrofitted frame, which protects the frame against seismic damage.

Structural health monitoring of civil structures: A diagnostic framework powered by deep metric learning

Recent advances in learning systems and sensor technology have enabled powerful strategies for autonomous data-driven damage detection in structural systems. This work proposes a novel method for the real-time localization of damage relying on a Siamese convolutional neural network. The method exploits a learnable mapping of raw vibration measurements onto a low-dimensional space, wherein damage locations can be easily identified. The mapping is learned in a supervised pairwise fashion exploiting labelled data, to induce a task-specific metric that allows to encode the damage position in the structure. Training data are generated through a reduced-order numerical model of the monitored structure. The damage position is then identified by performing a regression in the resulting low-dimensional features space. The proposed method does not require to define a priori target classes and decision boundaries, thus requiring a limited amount of user-dependent assumptions. Results relevant to an L-shaped cantilever beam and a portal frame railway bridge demonstrate that the procedure can be effectively exploited for the purpose of damage localization. The method also proves to be insensitive to operational variability, measurement noise and modeling inaccuracies.

Approach for early-warning collapse of double-span steel portal frames induced by fire

The unexpected collapse of burning buildings has posed a great threat to firefighters. Hence, early-warning methods for fire-induced collapse are urgently needed to avoid secondary casualties. This paper proposes an early-warning approach for predicting the collapse of double-span steel portal frames based on real-time measurement of displacements and displacement velocities of the burning frame. Firstly, numerical models are established to simulate the collapse behavior of double-span steel portal frames under fire, and six collapse modes of the frames are summarized through parametric analysis. The displacements and displacement velocities of the apex, eaves, and mid-span of rafters, defined as the key monitoring physical parameters (KMPPs), are found to have a close relationship with the collapse mode and time of the burning frames. Secondly, by exploring the rules of the KMPP-time curves, the characterized points that can be used for early warning of the collapse of the frame are extracted. Then, the early-warning approach applicable to six collapse modes is proposed based on the emergence of various characterized points. For universalizing the collapse prediction, early-warning time ratios are introduced and determined according to the reliability theory. Finally, the practicability and accuracy of the proposed approach are validated by an existing fire test.

Nonlinear mode saturation in a U-shaped micro-resonator

Saturation is an intriguing phenomenon that has captured the attention of scientists since the time of Froude when he reported it for ship motion in the mid of the nineteenth century. This work presents the demonstration and a comprehensive study of the nonlinear saturation phenomenon on a compound micromachined structure of U-shape (micro portal frame). The frame is designed and fabricated as a multi-input and multi-output device for actuating the 1st (sway) and 2nd (symmetric) in-plane vibration modes. Geometric nonlinearities along with the softening effect of the electrostatic force present the necessary conditions for the activation of a 2:1 internal (auto-parametric) resonance between the 1st and 2nd modes. Experimental data complemented with analytical simulations are obtained showing the internal resonance and the saturation phenomenon. These results are promising for further exploration of such compound structures and for further in-depth studies of the saturation phenomenon on a variety of other systems and applications.

A novel tension strap connection for rapid assembly of temporary timber structures

Emergency temporary housing is a critical component of post-disaster response and recovery. Their successful deployment requires structures to be low cost, easy to assemble, and with a capacity to adapt to local material and manufacturing availability. This paper proposes a novel ‘strap joint’ for the rapid assembly of lightweight timber elements and prefabricated panels. The joint utilises a low-cost and widely available packaging strap material, tensioned around timber elements to form a semi-rigid, adaptable structural connection. Experimental, numerical, and theoretical studies were conducted to evaluate joint semi-rigid structural behaviour. Joints are observed to possess a non-linear and highly ductile moment–rotation response, that arises from tension strap elongation, timber local bearing, and joint rotational deformation. A portal frame numerical model and full-scale physical prototype are also developed to contextualise the utility of the proposed strap connection for an emergency housing application.

Comparative Life Cycle Analysis of Timber, Steel and Reinforced Concrete Portal Frames: A Theoretical Study on a Norwegian Industrial Building

The construction industry is a big contributor to greenhouse gas emissions, which has a negative environmental impact. Several studies have highlighted the possibility of using timber to reduce the environmental impact of construction. Most of these studies have focused on residential buildings, but little attention has been devoted to industrial buildings. In this paper, an attempt is made to compare the environmental impact of using timber, steel, and reinforced concrete in industrial buildings using life cycle assessment. The system boundary was set to cradle-to-gate with transportation to construction site due to the limitation of data, and only the quantities of the main structural system are considered. Portal frames with variable spans were designed using the three materials to meet similar load carrying capacity. Reinforced concrete was used in the foundation of all frames. The results of the comparative study show that timber has, by a good margin, better environmental impact than reinforced concrete and steel, due to the carbon stored in the wood. The results also show that reinforced concrete and steel alternatives have similar environmental impacts. The findings of this study agree with the findings of other studies on residential buildings.

Study and Design of Sports Stadium

Sports Stadiums, like many other civil engineering structures, are being pushed to their limits in terms of slenderness and structural efficiency. Sports stadium structure should be designed with the care of economic aspects as well as safety aspects. The objective of the study includes comparative analysis and design of CC structure as well as steel structure for sports stadium with keeping in view of weight and cost aspects. This report mainly covers analysis and design aspect of outdoor sports stadium. First chapter is for introduction regarding stadium type of structure. Basic requirements for the sports stadium are explained in this chapter. It covers the general aspect of sports stadium structure. Objective of the study, organization of report and problems formulation are included in the same chapter. Eden Garden Stadium is one of the largest stadiums in India. It has been selected for this particular study. Static and dynamic analysis of stadiums structure is included in the Third chapter. It covers the analysis of lower tier as well as upper tier gallery of G-Block of Eden Garden Stadium. Dynamic analysis has been carried out on various model of stadiums tierstructure Alternative structural system for the seating bowl is included in the fourth chapter. It covers the analysis and design of RCC and steel structural along with their comparisons. Comparisons mainly focused on cost and weight aspects of stadium structure. Alternative structural system for the roof structure is included in the fifth chapter. Cantilever portal frame has been taken as alternative option of space frame. Analysis and design of both the structure along with their comparisons is given in this chapter. Generation of geometry for the stadium structure using software like STAAD and design of various element of stadium structure are time consuming procedure. Computer program has been developed for the same. Explanation of computer program along with sample output for each design elements is given in the sixth chapter. Summary of report and conclusion along with further scope of work is presented in the seventh chapter.

Modern cladding systems for big sheds: The emerging state of the art

Stressed skin theory was first introduced in the 1960’s and intensive development continued until the mid-1980’s. This development was characterised by extensive research into the behaviour of low-rise portal frame structures clad with a single skin of profiled metal sheeting. The resulting state of the art was formalised in ECCS (1995). Since then, frames have become much taller and more slender while alternative cladding systems have proliferated. About 10 years ago, the construction industry in the UK was shaken by a small number of failures in the roofs of ‘Big Sheds’ clad with sandwich panels. Investigation by numbers of experts was inconclusive and non-disclosure orders (NDO’s) were issued by the companies concerned. In the UK, the Standing Committee on Structural Safety (SCOSS) was informed of this and, after discussion with the Institution of Structural Engineers issued an Alert entitled ‘Effects of scale’ (SCOSS, 2018). This drew attention to the fact that validation of our current design rules has been largely based on years of satisfactory building performance. However, such evidence may not be indicative of satisfactory performance as structures increase in scale. In deference to the NDO’s, a research program has been commenced based entirely on structural mechanics without making any direct reference to either forensic evidence from the sites of the failures or test results etc. that are not in the public domain. This is one of the papers arising from this research. It recognises significant deficiencies in the design procedures in the European Recommendations (ECCS, 1995) and the need for a full, non-linear, 3D numerical analysis of the complete clad structure. This, in turn, has resulted in the development of the ‘component method’ of analysis for structure cladding interaction problems that concentrates on the development of numerical models together with the performance of their ‘components’. The main alternative cladding systems are considered in turn and their characteristics and potential failure modes identified.

SHM under varying environmental conditions: an approach based on model order reduction and deep learning

Data-driven approaches to structural health monitoring (SHM) have been recently shown to be a powerful paradigm, helping to lead to an evolution of traditional scheduled-based maintenance methodologies towards condition-based ones. Nevertheless, only few of them provide monitoring scenarios accounting for the varying loading and environmental conditions, which can potentially lead to misinterpretations of the structural state. In this paper, we propose a damage localization strategy that efficiently exploits vibration and temperature data to account for the effects of temperature fluctuations on the structural response. By allowing for a finite number of a priori defined damage scenarios, deep learning techniques are used to handle the damage localization task as a supervised classification, conditioned on temperature data. The training dataset is generated through a parametrized thermo-mechanical model of the structure, under a prescribed variability of loading and thermal conditions. To relieve the computational burden associated to the data generation process, a parametric order reduction strategy is also exploited. Results relevant to two case studies, a cantilever beam and a portal frame, are adopted to testify the capability of the proposed procedure to locate the damage, also when characterized by a rather small reduction of the local stiffness properties.

System-based reliability analysis of stainless steel frames subjected to gravity and wind loads

In the process of developing the next generation of design standards for steel structures, most relevant international structural codes including AISC360, AISC370, AS/NZS4100 and Eurocode3 already incorporate preliminary versions of system-based design-by-analysis approaches that allow a direct evaluation of the strength of steel and stainless steel structures from advanced numerical simulations. As a result, recent research works have focused on building rigorous structural reliability frameworks to investigate acceptable target reliability indices for structural systems and to develop new design methods in conjunction with adequate system safety factors and system resistance factors. Although design recommendations exist for the direct design of hot-rolled and cold-formed steel structures based on advanced finite element analysis, the extension of the method to other materials such as stainless steel is under development. This paper is part of a research effort to build a reliability framework for stainless steel structures subject to different load combinations and presents the results of system reliability calibrations carried out on six stainless steel portal frames subjected to combined gravity and wind loads. The study covers the most common stainless steel families and three international design frameworks (i.e., Eurocode, US and Australian frameworks). From the reliability calibrations derived, suitable system safety factors γM,s and system resistance factors ϕs are proposed for the direct design of stainless steel frames under combined gravity and wind loads using advanced numerical simulations.

Environmental impacts of Design for Reuse practices in the building sector

Actors of the construction sector are facing the challenge of reducing their carbon footprint and ideally reaching carbon neutrality. Reuse of structural elements made of concrete is of particular interest, given the large use of this material worldwide and its high environmental impact. Reusing constructive concrete elements is however challenging, particularly because connections between concrete structural elements are difficult to disassemble. It is then worth designing reuse techniques for concrete load-bearing elements and to verify their environmental performance using comprehensive methods such as Life Cycle Assessment. Based on the Design for Reuse concept, this article assesses the environmental impacts of a reusable structural portal frame constitutive of a concrete building and compares it to a traditional design with new materials. It relies on data collected through an experimental protocol of reinforced concrete structures construction/deconstruction/reconstruction using hydrodemolition. Impact scores are significantly reduced for all environmental categories after a first reuse cycle, both at the scale of a portal frame or a building. Concrete, and particularly high performance concrete, has durability qualities allowing to undergo several usage cycles. The effectiveness of environmental benefits however depends on functional downgrading and material losses. Guidance should then be provided to insure that future reuse practices will actually provide the expected benefits. This has to be conducted in parallel to full-scale experiments of load-bearing elements disassembly to estimate the realistic rates that can be obtained when deconstructing a building.

Multifiber finite element model based on enhanced concrete constitutive law to account for the effects of early age damage on the seismic response of RC structures

RC structures get damaged over time due to several phenomenons such as shrinkage, thermal deformations, creep and corrosion. This damage starts at early age and continues during the lifetime of the structures. In order to account for the effects of early age damage on the seismic response of RC structures, a research project combining both an experimental and numerical part was conducted. In the experimental part, two types of portal frames that evolved either in endogenous conditions (by covering them using a plastic sheet to limit drying shrinkage) or in non-endogenous conditions (no imposed covering, thus similar conditions as in site constructions) during early age, were constructed and tested at the end of 28 days using static cyclic and pseudo-dynamic tests. Experimental tests performed and monitoring techniques used (ambient vibration, digital image correlation, optical fiber) showed that early age drying shrinkage can cause an increase of the seismic vulnerability of RC structures (50% decrease of the fundamental frequency, 33% lateral drift increase). This article presents the multifiber finite element model based on enhanced constitutive law which allows describing the early age damage due to shrinkage, creep, thermal and mechanical strains and to simulate the static and dynamic response of the portal frames. The resolution of a THC (Thermo-Hygro-Chemical) problem allows calculating shrinkage and temperature time evolutions. In the model, creep is calculated using three viscoelastic Kelvin Voigt models in series with the μ damage law for concrete (through the resolution of an internal equilibrium at the fiber level) whereas steel is accounted for using a Menegotto model. Results obtained using the numerical model were compared to experimental ones in order to validate the proposed model.

Laboratory Model Test of Fully Buried Portal Frame-Shaped Slope-Stabilizing Piles

Abstract Fully buried portal frame-shaped piles have been widely used to control and stabilize large-scale landslides or slopes. However, the working mechanism of portal frame piles, such as the soil–pile interaction and load transfer behavior, is still not fully understood, which has limited the development of effective pile designs and construction. In this study, a well-designed laboratory model test was conducted in a sandy soil slope with a man-made slip surface. Nine portal frame piles were installed, synthetically considering the pile spacing between the rear and front piles as well as the support condition of the pile ends. To make the test closer to reality, in addition to a small thrust due to the excavation of the slope, greater landslide thrusts were imposed on the rear side of the portal frame piles by gradually applying static loads on the top of the slope. It is found that in addition to a concentrated thrust transferred via the cap beam, a landslide thrust accounting for 30 to 60 % of the landslide thrust on the rear pile was transmitted to the front pile by the soil sandwiched between the rear and front piles, which should not be ignored in designs. Meanwhile, to evenly mobilize the bearing capacity of both the rear and front piles, the reasonable spacing between them should be 1.0 to 1.5 times the diameter of the pile. The study also shows that portal frame piles should be embedded in a stable soil layer rather than the bedrock if they can meet the requirements for bearing capacity.

Brief Analysis of the Design of Composite Structure of Steel Frame and Portal Frame

Brief Analysis of the Design of Composite Structure of Steel Frame and Portal Frame

Seismic behaviour of prefabricated self-centring steel frames with different energy dissipation devices

The primary objective of this study was to obtain realistic and intuitive time-history seismic responses of three high-rise self-centring steel frames by performing contrast analyses. The prospective structural system of prefabricated self-cantering steel frame (PSCSF) has been proposed. The PSCSF reflects an evident advantage in controlling structural damage and eliminating residual deformation coupled with a great potential in terms of its applicability to high-rise buildings. However, negative effects were exerted on the generalization and application of PSCSF owing to the limit value in high intensity earthquake-prone areas not being satisfied. Based on PSCSF, a prefabricated self-centring steel frame with slit steel plate shear walls (PSCSF-SW) and a prefabricated self-cantering steel frame utilizing intermediate column dampers (PSCSF-IC) have been depicted. Several tests focusing on the nodes and portal frames regarding PSCSF, PSCSF-SW and PSCSF-IC already conducted were considered while presenting a new modelling approach in this paper, which was proven to be reliable in simulating portal frame of PSCSF-SW. Assuming that the results of numerical model showed high correlation with test results, three high-rise buildings of PSCSF, PSCSF-SW and PSCSF-IC were generated using finite element software ABAQUS. Consequently, modal and dynamic time-history analyses on three frames were performed to comparatively analyse the seismic performance under three ground motions with different peak ground accelerations. The derived PSCSF-SW and PSCSF-IC were found to reveal higher stiffness and more energy dissipation than the PSCSF. The outcome demonstrated that the setting of slit steel plate shear walls and intermediate column containing friction dampers resulted in reliable and feasible protection of the main components of high-rise self-centring buildings from being damaged and simultaneously resolved the problem of relatively large horizontal displacement of PSCSF being observed. Consequently, the PSCSF-SW and PSCSF-IC are expected to be competitive options for high-rise buildings. Because of the advantages of high-efficient assembly and replacement, the PSCSF-SW takes on more practicality and flexibility than PSCSF-IC.

Modelling and Seismic Response Analysis of Non-residential Existing Steel Buildings in Italy

ABSTRACT Non-residential older buildings usually have a significant role in the economy of a territory, making their seismic response worth of investigation. To this end, archetype steel buildings were selected, with portal frames and stabilizing braces. Non-linear models were developed including brace buckling and fracture, connections, cladding panels. Both static and dynamic analysis were carried out considering three building sites and two performance levels: usability-preventing damage and global collapse. Results show significant effects of the structural choices on the seismic performance, depending largely on the connection characteristics. Especially, the cladding connections largely affected the exceedance of the usability preventing damage level.

Stability Analysis for Spatial Autoparametric Resonances of Framed Structures

The spatial dynamic instabilities of framed structures due to autoparametric resonances have been seldom investigated in the published literature. Based on the finite element method (FEM), the spatial parametric vibration equations are established for general framed structures. The Newmark’s method and the energy-growth exponent (EGE) are used to determine the stability of the spatial autoparametric resonances of framed structures. A portal frame model is used to conduct a spatial (out-of-plane) autoparametric resonance experiment. The numerical results of the autoparametric resonances are found to agree with those of the test, which proves the validity of the present theoretical formulation. A numerical example for autoparametric resonance stability analysis of a spatial frame is presented to firstly predict the three instability modes of autoparametric resonances, i.e. global unidirectional translational instability, bidirectional (diagonal) translational instability and torsional instability. When the excitation frequency is approximately twice the modal frequency of spatial vibration of a framed structure, spatial dynamic instability will occur due to autoparametric resonance. A small excitation force can cause a strong autoparametric resonance of the framed structure. The potential risk of spatial dynamic instability is revealed for the framed structures under periodic loads.