Horizontal Members Research Articles

A refined cylinder fire model for thermal radiation calculation from localized fire to exposed horizontal surface

Fire is the most frequent hazard to buildings. The current design methods for predicting the temperatures of structures in fire are originally developed for the standard fire that assumes a uniform gas temperature field and are invalid for natural fires with high non-uniform gas temperature fields. Localized fire is a typical natural fire with high non-uniform gas temperature field, which is often considered in fire safety design. There are currently no validated simple general models for calculating the heat transfer from localized fire to exposed structures. To address the need of design method, this paper develops a refined cylinder fire model for calculating the incident radiant heat fluxes on horizontal structural members inside and outside the flame region of a localized fire. The model uses a cylinder, centered at the fire plume axis, to represent the localized fire. The height of the cylinder is not fixed, different to any other fire models. The temperatures in the cylinder are highly non-uniform in three dimensions and are determined based on the classic fire plume theory. For radiation calculation, the cylinder is evenly divided into several elements along the radius and height. Each element is assumed to be a homogenous, isotropic, and absorbing-emitting (participating) graybody. By careful consideration of the spatial gas temperature distribution, the radiation properties (emissivity and transmissivity) of the elementary graybody, and the configuration factor between the elementary graybody and the horizontal target surface, the model can get relatively accurate and conservative incident radiant heat flux. The relative deviations against both the experiment data and numerical results are within ± 30 %. The model introduces a new concept of calculating the heat fluxes from fire to structures, is a relatively simple general model (compared with the sophisticated computational fluid dynamics models), and is more precise and accurate than other simple ones. The model is recommended for use in performance-based fire safety design.

Shear Bearing Capacity of Steel-Fiber-Reinforced Concrete Shear Wall under Low-Cycle Repeated Loading Based on the Softened Strut-and-Tie Model

In this paper, the loading mechanism of steel-fiber-reinforced concrete (SFRC) shear wall (SW) under low-cycle repeated loading is analyzed, and the softened strut-and-tie model (SSTM) of SFRC SW composed of horizontal and vertical resistant members and diagonal strut is proposed, in which the contributions of distributed web reinforcement, concrete, and steel fiber (SF) to the shear bearing capacity (SBC) of SFRC SW is identified. Furthermore, a new algorithm to obtain the SBC of SFRC SW is established, and then it is validated by using the test results of steel-fiber-reinforced high-strength concrete (SFHSC) SW and SFRC SW under low-cycle repeated loading. The results show that the calculated values are in good agreement with the experimental values for the 11 SFRC SWs, and the average strength ratio between calculated and experimental values (Vjh,t/Vjh,c) is 0.958. Therefore, the proposed calculation method is scientific and accurate for analyzing and predicting the SBC of SFRC SW. In addition, the proposed calculation method can scientifically and accurately analyze and predict the SBC of SFRC SW.

Analysis and Application of Double Steel Plate Concrete Composite Shear Wall in the R&D Building of Zhanjiang Bay Laboratory

The R&D Building of Zhanjiang Bay Laboratory is a high-rise structure with multiple irregular items exceeding the specification limit, employing a steel frame-shear wall structural system. The outer frame consists of square steel tube concrete columns and solid-web steel beams, while the core shear wall uses a double steel plate concrete composite shear wall. This paper employs the architectural structural calculation software YJK-EP to perform a dynamic elastic-plastic time-history analysis under rare earthquake action. The shear and bending resistance of the shear wall at the maximum shear force and bending moment are checked to meet the requirements of the “Technical Specifications for Concrete Structures of High-rise Buildings”. The maximum inter-story displacement angle meets the requirements of the “Code for Seismic Design of Buildings”. The double steel plate concrete composite shear wall Wall-1, connected to a large-span and heavy-load transfer truss, was verified under significant seismic action using the ABAQUS software. The results indicate that Wall-1 can meet the design target requirements under major earthquake conditions. Finally, a dynamic nonlinear analysis method was employed using MIDAS-GEN software to study the structure’s anti-progressive collapse performance. The results show that under seven different scenarios, the maximum rotational angle of the remaining structural horizontal members is 2.02°, far less than the limit set by GSA, indicating that a progressive collapse did not occur. In the scenario where the corner column is removed, both the maximum shear and bending moment values for Wall-1 are far below its shear and bending resistance capacities, satisfying the load-bearing requirements. The removal of the corner column has a significant impact on the displacement of the columns on the same level nearby, with the peak displacement change rate reaching 702.65%.

Failure mechanism of a Q690 steel tubular transmission Tower: Full-Scale experiment and numerical simulation

The failure mechanism of a Q690 steel tubular transmission tower is investigated through full-scale experiment. The tower is mainly subject to the influence of the wind and the loads from the transmission lines. The displacements and the strains of the key positions as well as the ultimate bearing capacity of the tower are thus obtained. The final collapse is induced by the buckling instability of the compressed main member of a tower leg. A finite element model is established, whose validity is verified by the experimental data. Then, the numerical model is used for further analysis on the structural responses of the tower. It is found that once plasticity occurs at a certain point on the main member, its lateral displacement would be much accelerated, thus amplifying the second-order effect thereof. The horizontal auxiliary members, connected to the bottom of the compressed main member, are initially under tension. While the deformation of the main member is aggravated, they gradually undergo the transition from tension to compression, constituting a lateral support to the main member. This support then enforces the plasticity to develop towards the middle section of the main member, resulting in the final failure at the same location as observed in the full-scale experiment. These findings are crucial for a progressive understanding of the failure mechanism of this type of high-strength steel tubular towers, and they have contributed to the optimization of the design method to prevent the collapse of transmission tower under similar circumstances.

Behavior of a Composite Steel Decking and Boarding System in Fire Based on Large-Scale Experimental Testing and Numerical Modelling

This paper presents experimental and numerical results of an investigation into the thermal and structural behaviour of an innovative modular structural steel system, which includes cellular beams, that was tested in a 1-h standard fire scenario while loaded. The modular system consists of a 5.66 × 3.8 m rectangular steel frame, with a profiled steel sandwich decking (SD) system attached, which comprises of (a) profiled steel decking, (b) fibre cement, and (c) calcium silicate boards and strips. The SD system is suspended from the underside of the horizontal structural members to provide inherent fire protection to the steel beams from the bottom and acts as the load-bearing component of the flooring. The purpose of the experiment was to determine the fire resistance of the structural system, whilst under load, which is primarily based on the fire resistance of the SD system. Temperature data for the SD system was collected during the experiment and used to validate a numerical finite element analysis model. This study shows that the SD system was able to achieve a fire resistance rating of 57 min in the experiment which was governed by insulation resistance. A lower fire resistance rating is estimated based on numerical models. Structural resistance was maintained throughout the test. During preliminary testing structural collapse was observed in a separate experiment which highlights how the system is sensitive to damage to the ceiling boards. Numerical results highlight that thermal bowing and movement may result in changes in thermal interactions between adjacent elements. This paper provides novel large-scale experimental data on a loaded flooring system in fire.

FRP retrofit for RC frame substructures against progressive collapse: Scheme optimisation and resistance calculation

Fibre-reinforced polymer (FRP) strips have been widely used to retrofit existing reinforced concrete (RC) frame structures to improve their progressive collapse resistance. However, existing FRP retrofitting schemes improve structural collapse resistance by simultaneously enhancing the tensile and flexural strengths of horizontal structural members. The enhancement in flexural strength may lead to an unfavourable strong-beam weak-column mechanism in the seismic scenario. Hence, existing FRP retrofitting schemes were optimised in this study by numerical investigation using LS-DYNA, and effective schemes against both progressive collapse and earthquake were identified for RC beam-column and beam-slab-column substructures. The identified schemes remarkably improved the structural performance against progressive collapse at large deformations whilst marginally affecting the progressive collapse resistance at small deformations to guarantee the strong-column weak-beam mechanism in the seismic scenario. Furthermore, based on the parametric analyses for 81 full-scale substructures, analytical methods were proposed to calculate the strength of RC frame substructures retrofitted with the identified schemes under catenary mechanism, which can be further used to design the FRP retrofitted RC frames.

Experimental Study on the Rotational Stiffness of Pocket Type Scaffolding Connection According to the Rotation Direction

The rotational stiffness of the pocket-type connection used in system scaffolding to join horizontal members and vertical members was evaluated. To investigate the rotational stiffness of connections when subjected to bending moments in the downward, upward, and lateral rotation directions, load tests were performed on 30 specimens with cantilever specimens for each rotational direction. Results showed that failure shapes of pocket-type connections were different depending on the rotation direction. Owing to the differences in the failure phenomena, the maximum moment capacity of the upwardly rotated specimens was the largest, followed by that of the downwardly rotated specimens and the laterally rotated specimens in that order. Compared to the Eurocode 3 connection classification, the pocket-type connections correspond to semi-rigid connections when the rotation direction is downward or upward, and they can be considered nominal pin connections when the rotation direction is lateral. From the moment-rotation curves, it was concluded that the rotational stiffness of the pocket-type connections could be estimated as a bilinear model.

Investigation of the Global Structural Behavior of the Prefabricated Shoring System Considering Structural Details

This study aims to investigate the structural behavior and load-carrying capacity of prefabricated shoring systems. The structural behavior and performance of shoring systems are influenced by the buckling of vertical members, where the compressive force acts as the main load. The buckling strength of a vertical member is sensitive to not only the material and geometrical properties of members but also the connection details between members, presence or absence of braces, and stiffness ratio between members. Therefore, in this study, the structural behavioral characteristics of the individual post member and the entire system are investigated by considering the structural details through eigenvalue and nonlinear finite element analyses. On the basis of the analytical studies, it was confirmed that the boundary condition of the vertical member, rotational and horizontal stiffnesses, and eccentricity condition of the end, which are directly affected by the compressive force acting on the prefabricated shoring system, have a direct effect on the elastic buckling strength. In addition, it was determined that factors such as whether the braces were installed, rotational stiffness of the vertical–horizontal member connection, and the number of installation stages affected the overall strength of the structure. According to the structural analysis results, the assembled structure was reduced by 92.9% and 82.2% compared to the elastic buckling strength of a single member as the height increased to two and three stories. In addition, when the bracing member was not installed, 12.1% and 23.6% strength reduction was confirmed as the elastic buckling strength increased by two and three stories compared to the case where the bracing member was installed. Consequently, the necessity of a whole structural performance evaluation technique was confirmed for a more practical structural performance evaluation.

Analytical Investigation of the Effects of Secondary Structural Members on the Structural Behaviors of Transmission Towers

High-voltage transmission towers consist of structures that are designed to avoid the risk of electric shock and prevent the risk of collapse. Hence, for efficiency, they are generally designed as high-rise towers. The main tower posts are the primary structural members that resist loads under various load conditions. Therefore, the contribution of the secondary members to securing the stiffness and strength of the main posts by reducing the effective buckling length is an important one. However, we lack detailed secondary member design criteria. In this study, we observed the structural effects of the horizontal members and braces on the torsional stiffness, elastic buckling strength, and load-carrying capacity of a transmission tower using various structural analysis methods, including linear elastic, eigenvalue, and geometric nonlinear and inelastic analyses, under governing load combinations. According to the analytical results, it is the brace spacing rather than the horizontal members that substantially affects the structural performance. Therefore, we can minimize the number of horizontal members if we erect sufficient brace members. If the brace spacing is wide, then the horizontal members should be erected to create K bracing, thereby enhancing the buckling resistance of the main posts.

Re-Entrant Honeycomb Auxetic Structure with Enhanced Directional Properties.

This paper presents a modified re-entrant honeycomb auxetic structure. The structure is constructed by adding an additional horizontal member between the vertical and re-entrant member of the semi-re-entrant honeycomb model to increase the overall compliance of the structure in order to obtain higher values of negative Poisson's ratio (NPR). An analytical model of the structure is presented, taking into account the bending, shear, and axial deformations. The model is verified using finite element analysis (FEA) and tensile testing. The results of FEA and tensile testing corroborate the results of the presented mathematical model. The structure is also compared to the existing re-entrant honeycomb structure. The newly added strut has shown a direct effect on the directional properties of the overall structure. With an increase in the newly added strut to re-entrant lengths, NPR was significantly enhanced in the x-direction and reduced in the y-direction loadings. The structure shows an improved Young's modulus compared to solid material in both loading directions, especially for the low values of the new strut and re-entrant lengths ratio. The structure also shows that high NPR can be achieved for low relative density compared to semi re-entrant honeycomb structure.

Unified Simplified Capacity Model for Beam-Column Joints into RC Moment Resisting Frame

Seismic vulnerability of reinforced concrete (RC) buildings is strongly influenced by beam-column joints. Horizontal and vertical structural members converge in beam-column joints, as extremely delimited areas where the internal forces in concrete core and reinforcing bars have elevated stress gradients. In order to fully understand the seismic behavior of RC buildings and the related failures of T- and X-shaped beam-column joints (external corner and internal-positioned), an analytical model of RC joint behavior is proposed in a unified and simplified way. The equilibrium equations of cracked joint portions allow the assessment of internal stresses’ evolution at increasing values of column shear forces. In this way, the strength hierarchy is evaluated in terms of capacity for the different potential failure modes. This can drive, as a useful tool for designers, the design of new efficient structures or the assessment of existing ones to occur, with subsequent interventions to move an initial undesired failure mode to a more suitable one. Nearly 500 experimental results of tests available in the literature are compared with the analytical predictions of the proposed model.

Structural behaviour of a novel modular cellular steel beam system at elevated temperatures based on large-scale experimental testing and numerical modelling

This paper presents experimental and numerical results of a modular structural steel system, encompassing non-composite cellular beams, that was tested using a 1-h standard fire scenario while loaded. The modular system consists of a 5.66 m × 3.8 m rectangular steel frame, with a sandwich decking (SD) system attached, which comprises of a) profiled steel decking, b) fibre cement, and c) calcium silicate boards. The SD system is hung from the underside of the horizontal structural members to provide inherent fire protection to the steel beams from the bottom and is the load-bearing component of the flooring. The aim of the experiment was to determine the structural systems fire resistance because its unusual geometry renders existing full-scale fire test data inapplicable. Novel temperature and deflection data for the system are obtained from the large-scale experiment conducted, which are used to validate numerical finite element analysis models on a single element and global model basis. The numerical and experimental data are compared and show suitable correlation, and highlight some unusual behaviour regarding vertical deformations. From the numerical models and experimental data, it is shown that (a) the structural steel system typically behaves well due to the limited temperature rise as a consequence of the attached SD system, (b) limited plasticity occurred in the system, (c) small axial forces are induced due to the flexibility of the structure, and (d) the system is heavily reliant upon the integrity of the sandwich decking system it supports. Failure of the SD would lead to loss of compartmentation, and potentially structural failure.

Experimental and Numerical Study on Dou-Gong Joint of Ancient Wooden Structure in Qing Dynasty

ABSTRACT Three full-scale Dou-Gong specimens at column tops are made according to the Qing Dynasty “code of engineering practice,” based on the prototype of one Dou and two Sheng Jiaomaye Dou-Gong of Jiayuguan tower. The three-dimensional load-displacement curve of Dou-Gong is obtained using three-dimensional static loading tests. Furthermore, the deformation characteristics, three-dimensional compression stiffness, and three-dimensional load transfer law of each layer of the Dou-Gong are analyzed. The test results indicate that the vertical failure characteristics of the Dou-Gong are the splitting of the Flat-Fang, and there is no obvious damage to the horizontal members until toppling. The three-dimensional load-displacement relationship curve of the Dou-Gong can be simplified to a two-fold line model, vertical stiffness of the Dou-Gong is significantly greater than the horizontal stiffness, and the horizontal stiffness in the beam direction is greater than the horizontal stiffness in the Fang direction. Using ABAQUS software, a comparative analysis of the difference in mechanical properties between the Dou-Gong at the column tops and the Dou-Gong between the columns is performed. The research results can provide a theoretical basis for the structural performance safety assessment and preventive protection of the Jiayuguan tower and similar Chinese ancient wooden structures.

Evoluzione della carpenteria lignea dei tetti in Grecia tra età arcaica e classica. Alla ricerca di tracce di incavallature

The paper analyzes the evolution of the organization of timber roofing carpentry in Greece and in the colonies of Sicily and Magna Graecia in a chronological scope between the archaic and classical periods. A substantial continuity, lacking evident innovations, characterizes the organization of the carpentry of the roofs constituted, in general, by a horizontal member on which rest on props – king and queen posts – coinciding with the purlins, useful for receiving the secondary framework and the roof covering. The lack of evident indicators, in a cognitive framework that is however extremely fragmented, and a constructive culture on timber that does not seem to excel for technological advancement raises many doubts about a possible pioneering use, even in constructions with high distance between supports, of carpentry organized as a truss system, with no pushing component on the wall.

Effect of Shape on the Temperature of an Opening Jet Plume at the Bottom of a Horizontal Member

In this study, combustion tests, in which the opening condition of a fire source was changed using a large-scale compartment and horizontal member, were conducted. The inner temperature, temperature distribution under the horizontal member, external flame shape, and neutral zone height of the compartment were measured under various opening conditions. The results were analyzed using the temperature prediction equation for the opening jet plume at the bottom of a horizontal member, proposed by the Architectural Institute of Japan (Building fire load and design fire property guideline (draft)), and a review was deemed necessary.

Stress analysis of I-beam with web opening via finite element analysis and experimental study

PurposeThe purpose of this work is to perform the finite element analysis (FEA) for the numerical discretization of sections with different arrangements of Web openings to investigate the torsion behavior. Typical hexagonal and circular Web opening sections are extensively used in steel construction due to economic development in building design. However, the use of sections with different arrangements of Web opening had improved the performance of the section with Web opening in terms of structural behavior which leads to economic design compared to typical I-beam.Design/methodology/approachThe accuracy of FE results allows extensive numerical analysis of stress concentration magnitude for sections with Web openings, concentrating on the sizes and positions of the Web opening. Five shapes and three sizes of Web opening are used in this work. The shapes involved are c-hexagon, hexagon, octagon, circular and square, whereas the sizes of the Web opening involved are 0.67 D, 0.75 D and 0.80 D where D is the height of the Web. Two types of models for 200 × 100 × 8×6 mm steel section involved which is Model 1, where the section with 50 mm edge and 150 mm center-to-center distance and Model 2, where the section with 100 mm edge and 200 mm center-to-center distance.FindingsIt was found that these configurations affect the section with various shapes of Web openings sizes (0.67 D, 0.75 D, and 0.80 D). This also includes the spacing distances, with 50 mm edge and 150 mm center-to-center distance and also a section with 100 mm edge and 200 mm center-to-center distance. Through the FEA results of Model 1 and Model 2, it is found that 50% reduction in horizontal member length in hexagon Web opening, from 50 mm to 20 mm, caused increment about 30%–53% stress concentration in Web for c-hexagon. However, for a stress analysis of c-hexagon, geometry resulted in a lower stress concentration in the Web than other Web opening.Originality/valueAdditionally, the work emphasized the efficiency of Web opening shapes by using an appropriate Web opening radius in section with c-hexagon, hexagon, octagon, square and circular shapes. The final results show the contribution of appropriate Web opening radius to increase the section torsional capacity. It is observed that the torsional capacity at certain loading condition and its angle of twist is analysed.

In–plane cyclic behaviour of half-timbered walls with fired brick infill

In this paper, the in–plane cyclic behaviour of half-timbered walls with fired brick infill, widely used in traditional half-timbered buildings is studied. Structural analysis is performed by the finite element ANSYS code assuming non-linear behaviour of materials. Micro-modelling approach is used with different properties for the timber and the masonry. Fifty-seven different models are analysed and compared in terms of load-bearing capacity and energy dissipation. The results of analysis show that vertical and horizontal wooden members of the wooden framework have little effect on changing the load-bearing capacity and energy dissipation. Diagonal wooden members sharply increase the load-bearing capacity and energy dissipation. Openings reduce the load-bearing capacity and energy dissipation. Because the diagonal wooden members significantly increase the load-bearing capacity of the wooden frame at the appropriate arrangement of diagonal wooden members, it is possible to reduce the duty of the masonry infill in lateral load-bearing.

Study on the Flexural Strength of Interior Thick Wall-Thick Slab Joints Subjected to Lateral Force Using Finite-Element Analysis

A brand-new structural type, termed thick wall-thick slab structure, has been developed in recent years based on the reinforced concrete wall structure in Japan. This type of structural system can not only maintain high seismic performance, but also provide large interior space and improve the flexibility of the architectural design that is more favored by architects. In the present study, an equivalent cross-sectional area concept in which a coefficient termed the equivalent cross-sectional area ratio is proposed to estimate the flexural strength of the horizontal member of the interior wall-slab joints, which are critical assemblies in the thick wall-thick slab structures. To capture the stress condition of slab flexural reinforcement for calculating the equivalent cross-sectional area ratio, the method of finite-element analysis was employed in this work. The finite-element modeling was calibrated firstly using two isolated interior wall-slab joints from literature and consequently applied to a parametric numerical study. Finally, results from these finite-element analyses are adopted to propose the equivalent cross-sectional area ratio for modifying the current code formula to predict the flexural strength of interior wall-slab joints in TWTS structures subjected to lateral force.

Fatigue Performance of Overhead Truss Sign Structure Coupler Connections

Nearly all aluminum overhead truss sign structures (OHTSSs) in Kansas constructed before 2015 use an identical type of hot-riveted coupling assembly to provide connections between vertical poles and horizontal truss members. Although many of the connections have been in service for 30 to 40 years, no research has been conducted to determine their fatigue performance. This paper presents a study aimed at characterizing the fatigue performance of the coupler connections. The study includes a series of finite-element (FE) analyses and 24 experimental fatigue tests. The FE analyses were used to determine design-level fatigue demands on the coupler connections and to provide information for designing the experimental setups used in this test program. Four sign structures with three connection properties and six loading modes were modeled. The experimental tests were conducted to characterize the fatigue performance of the connection. Tests were conducted for three loading modes with respect to the load on the rivet connecting the two interior half-couplers: (1) tension, (2) vertical shear, and (3) horizontal shear. Results indicated that when loaded below 10 Ksi (68.9 MPa), the connection can be classified as a Category E′ based on stress in the rivet. The FE analyses and test results indicated that fatigue failures are unlikely to occur in the coupler connections used in OHTSSs. In addition, two used coupler assemblies from OHTSSs taken out of service were also tested and the failure surfaces were examined under a microscope. No reliable evidence of preexisting cracks was found.

A Modified Compression Field Theory Based Analytical Model of RC Slab-Column Joint without Punching Shear Reinforcement

RC slab–column structures are widely used because of the advantages of small space occupation for horizontal members, easy construction and good economy. However, slab–column joints are prone to punching shear failures, which deteriorates structural safety. This paper provides an analytical model to predict the punching shear capacity of the RC slab–column joint. A database of 251 test results is established for the shear punching capacity of slab–column joints without punching shear reinforcement. The performance of existing design codes in predicting the shear resistance of slab–column joints is investigated and compared based on the database. Then, based on the modified compression field theory (MCFT) model, an equation for calculating the punching shear resistance of slab–column joints without punching shear reinforcement is established. The prediction results of the analytical model are enhanced by using the regression analysis method. The model proposed in this paper is based on both reliable theoretical and the summary of a large number of test results, which has higher prediction accuracy than the design codes.