Portal Frame Research Articles

A multi-fidelity surrogate model for structural health monitoring exploiting model order reduction and artificial neural networks

Stochastic approaches to structural health monitoring (SHM) are often inevitably limited by computational constraints. For instance, for Markov chain Monte Carlo algorithms relying upon computationally expensive finite element models it is almost infeasible to sample the probability distribution of the structural state. To provide instead real-time procedures, this work proposes a non-intrusive surrogate modeling strategy, leveraging model order reduction and artificial neural networks. By relying upon a multi-fidelity (MF) framework, a composition of deep neural networks (DNNs) is devised to map damage and operational parameters onto time-dependent sensor recordings. Such an effective strategy is able to exploit datasets characterized by different fidelity levels without any prior assumption, allowing to blend a small high-fidelity (HF) dataset with a large low-fidelity (LF) dataset, ultimately alleviating the computational burden of supervised training while ensuring the accuracy of the approximated quantities of interest. The resulting surrogate model is made of an LF-DNN, which mimics sensor recordings in the undamaged condition, and of a long short-term memory HF-DNN, which adaptively refines the approximation with the effect of damage. An HF finite element model and an LF reduced order model are adopted offline to generate labeled training data of different fidelity, respectively in the presence or absence of a structural damage. Results relevant to an L-shaped cantilever beam and a portal frame railway bridge prove that the procedure efficiently provides remarkably accurate approximations, outperforming their single-fidelity counterparts. The capability of the MF-DNN to be exploited for SHM purposes is finally shown within an automated Bayesian procedure, aimed at updating the probability distribution of the structural state conditioned on sensor recordings, in the presence of operational variability and measurement noise.

Analysis of Earthquake-Resistant Portal Frame Structures with Ordinary Moment Frames (OMF), Intermediate Moment Frames (IMF), and Special Moment Frames (SMF) based on SNI 1726:2019

Since the 19th century, portal frames have been used to build industrial buildings because the development process is fast, economical, and efficient. This research aims to look at the cross-section of structural elements in BS 5950-1:2000 spans of 15 m and 40 m using SNI 1726:2019 with modal analysis, including horizontal deflection and stress ratio, using LRFD and ASD methods. Then, the structure was revised to be safe against earthquakes researched in three zones, including low (OMF), medium (IMF), and high (SMF) earthquakes. The results of this research show that the horizontal deflection's magnitude still falls within the allowable limit, with the maximum value on Tarutung, the SMF system, and KDS E on a 15-m span of 43.828 mm and a 40-m span of 68.703 mm. However, several of the IMF and SMF systems' cross-sectional structures exceeded the stress ratio capacity. After revision, the percentage ratios of the maximum structural weight using cross-sections on the Indonesian market using two methods and three frame systems with spans of 15 m and 40 m are 16.050% and 17.240%, respectively. The obtained maximum structural weight exceeds the cross-sections of the British standard before revision by 13.935% and 13.187%. It is an SMF system.

Synchronous Displacement Acquisition Approach for Early Warning of Fire-induced Collapse of Steel Portal Frames

Synchronous Displacement Acquisition Approach for Early Warning of Fire-induced Collapse of Steel Portal Frames

Design of partial height web stiffeners in beam-to-column joints and influence of residual stresses induced by welding

Fixed beam-to-column joints in steel portal frames with bolted connections typically present stiffeners to ensure proper load bearing resistance and stiffness to the joint. Executing the same stiffeners with a reduced height (e.g. partial height web stiffener) allows for cost saving during manufacturing but must be paid off by considering its effects in the design verification of the joint. The usual gap size of the partial stiffener has a height of 10%–30% of the concerned element web depth. Based on the Astron product example, this study analyzes the effects of the partial stiffener on the concerned knee joint resistance components according EN1993-1-8. A numerical parametric study is performed based on an advanced 3D FEM model to determine and compare the structural behavior of the beam-to-column joints with full and partial stiffeners. Comparison of the calculation results prove, the partial stiffener influences only the shear panel resistance component, and it has no effect on other components of the joint. The failure mechanism of the shear panel using different slenderness ratios are analyzed in the paper and an enhanced design method is developed, which allow to consider the geometrical gap between the flange and stiffeners. The effect of residual stresses resulting from the manufacturing processes of the plated elements is also analyzed and introduced in the paper using advanced weld simulation technique.

Numerical Analysis of Modified PVA Fiber Rubber Concrete in Frame Beams

The feasibility of PVA fiber rubber concrete modified by modifier in the structure was investigated using the portal frame as the research object. The basic mechanical properties of modified PVA rubber concrete materials were tested mechanically first, and then ABAQUS was used to establish the ordinary concrete portal frame model, and after confirming the model’s rationality, the rubber concrete, PVA rubber concrete, and modified PVA rubber concrete models were established on this basis, and the displacement and strain comparison analysis with ordinary concrete was carried out. The simulation results show that using PVA rubber concrete material in the concrete frame structure can improve the large deformation of rubber concrete, and using PVA rubber concrete treated with a modifier can improve structural strength and deformation even more.

Embodied Carbon Minimization for Single-Story Steel Gable Frames

As the construction industry, especially steel construction, contributes to a large portion of global greenhouse gas emissions, sustainable structural design has become a necessity to achieve the world vision of reaching net zero emissions by 2050. As steel portal frames are the most used structural system for single-story buildings, the main objective of this study is to determine the optimal steel portal frame configuration using prismatic and/or non-prismatic members to achieve the least embodied carbon. Five different portal frame configurations are considered under the effect of five distinct loading conditions. The results led to developing design charts consisting of contour plots showing the embodied carbon per unit of volume enclosed by the steel frame for different frame configurations, loading conditions, span lengths, and column heights. In addition, by increasing the number of member divisions, design variables, and non-prismatic segments, the average embodied carbon of the steel portal frames can be significantly reduced by about 14.34% up to 26.47% relative to the configuration with only prismatic members.

Cyclic Response of Sloped Extended End-Plate Moment Connections

Bolted extended end-plate (BEEP) moment connections are extensively recommended in design standards to be used as a prequalified beam-to-column connection in steel portal frames and special moment frame buildings. These standards assume that in such a connection, the beam is perpendicular to the steel column or that the slope angle of the steel beam is very small. To expand the engineering applications of BEEP connections in large-slope angle buildings, in this study, three one-sided specimens at half scale with 0°, 15°, and 30° slope angles, respectively, were designed and tested under cyclic loading. All dimensions of these specimens were identical, except the slope angles of their steel beams. The experimental results showed that the maximum rotation angles of these sloped BEEP connections exceeded 0.05 rad, and they were remarkably larger than those of other types of sloped rigid-moment connections tested by Mashayekh and Uang. However, the force concentration that occurred in the flange at the heel location was similar to that observed by them, and it led to the development of brittle fractures. Particularly, with the increase in the slope angle, the force concentration tended to become more severe. Three strengthening schemes for reducing the force concentration and enhancing the deformation capacities of the sloped BEEP connections subjected to the extremely rare earthquake, i.e., less than 2% probability of exceedance in 50 years, were evaluated using the finite element approach. These were Scheme I: stiffening the rib in the acute-angle zone, Scheme II: employing a reduced beam section (RBS) connection, and Scheme III: forming a curved web cut in a non-RBS beam. The analytical results showed that the three schemes decreased the von Mises stress level in the acute-angle zone of the connection web. Scheme I enhanced the initial rotation stiffness, flexural strength, and deformation rotation capacity. For Scheme II, a RBS configuration was employed, which effectively improved the connection rotation capacity, whereas it decreased the flexural strength of the sloped BEEP connection. Scheme III without a reasonable design led to a degradation of the hysteretic performance, moderate rotation capacity, and low flexural strength. Therefore, Schemes I and II leading to much better seismic behavior than Scheme III are recommended.

Rafter-purlin connection stiffness impact on the stress skin effect of corrugated sheet claddings

The paper analyzes the rafter-purlin connection flexibility, and its influence on the stressed skin effect of the corrugated sheet claddings. The study of these connections is important, because mainly gravity type loading experimental data are available. Stressed skin design code offers guidance for experimental results conducted on a single purlin profile (1Z), but the sample connections do not cover the nowadays most widely used details (2Z with overlaps). The preferred way for obtaining rafter-purlin connection flexibilities is experimental testing. To address the problem with a precise and relatively time efficient method, finite element models of some tested connections have been created and validated. Using the calibrated model configuration, a detailed parametric finite element analysis was conducted on the most widely used roof cladding details. Based on the results of a large set of calculations with varying geometrical parameters, using a precise bivariate quadratic interpolation, a set of 12 contour plot representations were created, that allows practicing engineers and researchers to obtain connection stiffness in a simple manner, saving a lot of time otherwise spent with testing or modeling. There is important decrease in flexibility when roof and/or wall purlins are overlapped due to the splicing. Generated results can be easily implemented in structural models of steel portal framed structures to account in the frame analysis the stiffness of the corrugated sheet cladding as stressed skin. A reliable method is presented for introducing the flexibilities of the purlin-rafter connections into a 3D portal frame structural model, considering the different connection stiffness in two loading directions. “Chameleon like” behavior of the roof cladding stiffness was observed, considering the structure-cladding interaction in the analysis. Using the improvements, weak and strong directional stiffnesses can be incorporated in the structural model and the difference between the single and overlapped purlin joints can be quantified. Also, with the provided data, the stressed skin design procedures update is possible.

Lateral resistance performance evaluation of cold-formed steel zero-tolerance bolted moment-resisting frames

The experimental and analytical lateral load resisting behaviour of three cold-formed steel (CFS) moment-resisting frames with zero-tolerance bolted joints were investigated to understand the potential application of such joints in medium-span CFS portal frames. Strain gauge data were used to measure total longitudinal stresses in the column sections and were compared with analytical models. It was found that the bi-moment stress component was the second largest component after major-axis bending and can be analytically and conservatively estimated. The validity of the design approaches of monosymmetric and doubly symmetric back-to-back channel columns were also investigated. For the first time, the potential application of zero-tolerance jointed frames in medium-span CFS portal frames is demonstrated and conservative analysis and design approaches (monosymmetric) are employed.

Moment capacity of apex brackets of cold-formed steel portal frames

The strength and stiffness of cold-formed steel portal frames are heavily related to the performance of their joints; these joints are normally formed through brackets, bolted to the webs of channels. They should have adequate strength to ensure the frame fails within the members, and the design moment capacity of a joint should be equal to or exceed the moment to which the joint is subjected. For apex brackets, based on the results of a non-linear elasto-plastic finite element study, the authors have recently proposed design guidance in the form of equations for predicting the moment capacity. However, this prediction was limited to fully restrained apex joints against lateral torsional buckling, which is an arrangement not commonly used in practice. Furthermore, the joints considered were composed of back-to-back brackets connecting back-to-back channels. The design recommendations were further limited to apex joints under bearing gravity load, equivalent to the opening moment applied to the bracket. This paper extends the previous work by now considering both single and double apex brackets, which are partially restrained, consistent with New Zealand practice, and considering both opening and closing moments on apex joints (or gravity and wind uplift load on portal frames). This study proposes unified design equations from a parametric study comprising 5,040 finite element models.

Optimization of Steel Portal Frames under a Parametric Structural Design Framework

This paper presents a framework for the structural design of single-story industrial steel portal frames. The structural mechanical utilization, stability, and serviceability design requirements employing a parametric structural tridimensional computational model are included. The model parameterization consists of adopting the column, rafter, purlins, and cladding span lengths as parameters, as well as the cross-section sizes of these members, the latter in accordance with the standard commercial cross section’s tables. The main outcome is the possibility to scan the range of parameters and store the structural performance ratios, generating a solution space for this structural system. This space of valid solutions attending structural code requirements defines a set of valid structural system topological configuration and dimensions, making it possible to obtain relationships between the parameters and material consumption rate. Concave-hull 2D plots are used to visualize the solution space and identify the best choice of parameters in the design process. It is shown that the solution space generation and the concave-hull 2D plots are powerful design aids that help to identify the best combination of structural system topological dimensions and cross-section types and dimensions.

Učinci oštećenja stupova na pouzdanost armiranobetonskih okvirnih nosača

The reliability and behaviour of columns belonging to portal-reinforced concrete frames depend on many factors. This paper presents a parametric study of a reliability column in a non-linear domain, considering mechanical variability and targeting damaged areas of the reinforced concrete columns. In this study, an adaptive method for assessing the reliability of columns with respect to damage states is proposed. The method is an indirect coupling of the response surface and finite element model in the non-linear domain. The main goal of this study was to provide a structural engineer with a modelling approach for optimal and robust column design. The results of the present study show that the reliability of columns belonging to portal frames is closely related to the quality of the constituent materials (steel and concrete) and the type of load applied. The reliability of this type of column also decreases with increasing load and applied displacement and increases with increasing compressive strength and yield strength of the steel. The uncertainties associated with the structural models are considered, with their impact on structure reliability studied using a sensitivity analysis, which allows the proposed approach to make the best possible decision for a better design and, therefore, good behaviour under different parameters.

Snap-interlock module system: Exploring an alternative architectural construction method

Responding to the rise of temporary architecture motivated by fast changing cultural and societal interests, construction methods must be adapted to meet the needs of reconfigurable systems. The prototype of Snap-Interlock Module System (SIMS) proposed in this study aims to integrate the simplicity of dry stacking as a primitive construction method through a coordinated joint system in order to increase material efficiency and structural integrity. This study explores a method of stacking blocks using unique interconnecting mechanisms without bonding agents to allow for reconfigurability. The considered unit of SIMS is configured to have four legs with integrated hooks on both top and bottom, allowing each block to snap into four adjacent blocks on either end. The centerpiece is designed such that each block can individually possess geometric versatility toward organic growth of the whole system. Larger assemblies of SIMS blocks can create full-scale structures without the use of bolting, welding, or other bonding agents. Finite element analysis demonstrates that the explored interlocking motion falls into the elastic range of the considered steel and confirms that structural integrity can be secured at the building scale as well. In order to test the proof-of-concept, 1:3 scaled Polylactic Acid (PLA) blocks are 3D printed and assembled into a 2.5 m tall portal frame, leading to a full-scale structural model executed with six full-scale steel blocks. The assembly and disassembly of both prototype structures are easily executed by a single individual. Despite the limitations of the chosen fabrication methods and material choices, the study promises diverse applications in the changing urban context and contributes to the broader sustainability of our built environment via an alternative and reconfigurable construction method.

Experimental and Numerical Assessments of New Concrete Dry Connections concerning Potentials of the Robotic Subtractive Manufacturing Technique

The efficient utilization of robotic construction of structures requires a review of structural material, elements and details, while traditional construction methods face difficulties in producing some dry concrete joints, robotic methods can manufacture them efficiently. With the rapid advancement of new construction methods, more effort should be directed towards developing new types of joints manufactureable by Additive Manufacturing (AM) methods. Accordingly, considering the potentials of robotic techniques, this article proposes eight new concrete dry joints. Concrete portal frames with two identical joints at the end of the beam are cast and evaluated under bending and shear. The performance of each joint, evaluated by experimental and numerical studies based on the crack distribution and stresses, was discussed. Furthermore, various aspects of the process of robotic subtractive manufacturing of the connections are discussed through the selected printed/milled geometries; likewise, geometrical accuracy by microscanning was measured, proving this technique’s capability (methodology). Based on findings, some proposed joints that can be manufactured entirely and quickly by robotic additive and subtractive techniques structurally can produce the full strength of the monolithic reference section. The range of the capacities and initial stiffness is, accordingly, [50%, 106%] and [51%, 124%] of the monolithic elements.

The Strength and Behavior of 3D Model Simulation of Single-Story Steel Industrial Building

The paper investigates the strength and behavior of the portal steel frame under the consideration of working 3D models. In terms of design, the industrial buildings have been separated into a single portal frame to simplify the design process. This point of view is suitable for structures in that the applied loads are equally distributed to all frames. The fact that the crane loads including vertical and horizontal loads only directly affected one or several portal frames. Therefore, a 3D model of a whole single-story steel industrial building is simulated in a finite element software program to study the internal forces and deformations of this building in comparison with those values of a model of a separated portal steel frame. Based on these comparisons, significant conclusions can be given, and recommendations are provided for designers.

Discussion on related problems in the design of portal steel frame

With the continuous acceleration of economic development speed, the construction demand of industrial plant is more and more large. In the construction process of the industrial plant, it usually adopts the portal steel frame and light steel structure, which is mainly due to the fact that the overall weight of this structure is light, the steel consumption is small, and the construction period is short. However, with the increasing application range of portal steel frame light steel structure, many problems existing in the design process are gradually exposed. On March 4,2007, more than 10 industrial plants and sheds collapsed in Tianjin under the influence of heavy snowfall. In this paper, the design of portal steel light steel structure. It is hoped that the quality of the design can be improved through the discussion of this paper.

3D numerical characterization of a dissipative connection system for retrofit of prefabricated existing RC sheds

Prefabricated industrial sheds featured a high seismic vulnerability during the 2012 Emilia earthquake (Italy). The buildings typically exhibited a rigid collapse mechanism that was a consequence of the loss of support between columns, beams and roof elements.The study presents a numerical characterization of a novel dissipative connection system (DCS) designed to improve the seismic performance of industrial sheds. The device, which is placed on the top of the columns, exploits the movement of a rigid body on a sloped surface to provide horizontal stiffness and control the lateral displacement of the beam.A 3D finite element model of the prototype is formulated in Abaqus and used to switch the backbone curve from the scaled model to the full-scale device. A parametric study is conducted to evaluate the influence of the slope of the contact surface and the coefficient of friction on the output force of the system.In the second part of the study, non-linear dynamic analyses are performed on a finite element model of a portal frame implementing, at beam-column joints, either the DCS or a pure friction connection. The results highlight the effectiveness of the DCS in controlling beam-to-column displacements, reducing shear forces on the top of columns, and limiting residual displacements that can accrue during ground motion sequences.

Comparative study of ANN and ANFIS models for detection of damages due to cracks in single bay framed structure

This paper presents damage assessment in steel portal frames through adaptive neuro fuzzy interface model and artificial neural network. In this study an attempt is made to find out the best models amongst the ANN and ANFIS techniques that give the most accurate results in detecting single and multiple damages due to crack formation. The tan hyperbolic sigmoid activation function with 5 hidden neurons gave the highest regression value of 0.982 when compared with the other ANN models. The Gaussian membership function gave the highest regression value of 0.9998 when compared with other ANFIS models. The performance of best models from both the techniques was evaluated and compared to identify the technique which gives the most accurate results. This comparative study concluded that, the ANFIS model with Gaussian membership function predicted the most accurate results in detecting the damages.

Field performance of an anti-uplift portal frame in control of the tunnel uplift induced by overlying excavation

Excavation above the tunnel will inevitably cause release of the ground stress and the associated tunnel uplift. The control of tunnel uplift is a tough problem that troubles the engineers. This paper introduces a new technology (namely anti-uplift portal frame technology) to control the tunnel uplift caused by long-distance collinear overlying excavation which adopted in the construction of an urban underground expressway in Shenzhen, China. The anti-uplift portal frame (AUPF) is composed of anti-uplift piles and anti-uplift slab, forming a portal frame between the bottom of the foundation pit and the tunnel to hoop the underlying tunnel. In order to minimize the impact of shaft excavation on the underlying tunnel during the AUPF construction, the AUPF was divided into sections in longitudinal direction and avoid excavation of the adjacent shafts at the same time. The field data indicated the median uplift after shaft excavation in the AUPF construction stage was 12.8 mm in Zone A and 5.3 mm in Zone B, and recovered by 62.5 % in Zone A and 85 % in Zone B after backfill. During the foundation pit excavation in expressway tunnel construction, the median uplift was 7.2 mm, recovered by 61 % after tunnel structure was constructed. When the tunnel uplift reached 8 to 8.5 mm, further excavation did not cause increase of the tunnel uplift, which indicates the AUPF can effectively control the tunnel uplift. The reported case provides valuable referrence to guide the similar overlying excavation projects.

On Structural Design of Steel Roof Truss Geometry Used in Factory Shed

Use of steel is steadily increasing all over the world in civil engineering related fields due to its superior material properties like high strength and durability, high ductility, light weight etc. Various types of steel structures become more popular because of their high aesthetic appearance. Among these steel structures, roof trusses are widely used to cover large column free open areas like shopping malls, auditoriums, car parking lots, stadiums as well as factory sheds etc. Design of steel truss members is an important aspect to the practicing civil engineers. Hence this paper aims to study the design and analysis of different types of truss geometries used in a factory shed using commercial well-established software package STAAD Pro V8i. Various types of truss geometries like Pratt truss, Howe truss, Fink truss are considered in the present investigations with different aspect ratios. Besides these truss geometries, portal frame geometry is also taken up here to examine the best suitable geometries which are to be used as roofing units in industrial purposes. The results obtained from the present numerical experimentations are studied meticulously to extract a set of meaningful conclusions regarding the design and optimum choice of steel truss geometry which is used as roofing units in industrial sheds. The practical design guidelines along with the best choice of roof trusses are highlighted in the results and discussions section of this paper.