Composite Floor Trusses, Design Considerations and Practice

A space frame is a skeleton structural system assembled using linear elements so arranged that forces are transferred in a three-dimensional manner. Architects and engineers aim for new structural forms to accommodate large unobstructed areas. Space frames satisfy the objectives, and it provides lightness, economy, and speedy construction. Previous research investigation in the composite space truss, proved that using concrete slab acting compositely with the top chord member is to reduce the buckling of the compression chord members and also improve the overall behaviour of the space truss sturctures. The advantages of the composite space truss, gives confidence to use as floor system in the multistorey buildings. The composite space truss is influenced by various design parameters like cross-sectional area of the tubular member, support condition, module size and their depth, concrete strength and concrete slab thickness. The analysis of composite and noncomposite space truss as roof as well as floor for the building of size 30 m × 30 m was carried out using ANSYS software for varying design parameters. The overall maximum central deflection for the models was observed and compared with the codal provision. The load–deflection behaviour of the models was plotted, and the optimal solution for the noncomposite and composite space truss was arrived.

This paper examines the performance and stability of steel–concrete composite systems used in the working towers of grain elevator facilities, subjected to dynamic effects originating from grain cleaning equipment. The research centers on evaluating the structural response of elevator towers with separator floors formed either from steel-only frameworks or composite slabs incorporating concrete and profiled sheeting. Particular attention is given to resonance susceptibility and methods to enhance structural integrity under operational conditions. Purpose. The aim of the study is to analyze and compare the dynamic performance of different flooring systems in grain elevator towers – steel-only structures versus steel–concrete composite slabs – and to assess their susceptibility to resonance caused by grain cleaning equipment. Methodology. The study employed modal analysis of two flooring configurations using computational modeling tools. Natural frequencies and corresponding mode shapes were determined via LIRA-FEM for both static and dynamic analysis. Autodesk Revit was used to develop the structural models. Resonance risk was evaluated by comparing computed natural frequencies with the known 5 Hz operational frequency of grain cleaning machinery. Results. The analysis revealed that composite floor systems using profiled steel decking and concrete slabs significantly reduce vibration intensity compared to steelonly floors. Variations in concrete slab thickness and shear connector dimensions were tested, resulting in improved dynamic behavior and structural stability. The natural frequencies of both systems were benchmarked to evaluate resonance potential. Composite floors showed better alignment with safety requirements and machine stability under dynamic loads. Scientific novelty. The study introduces the application of steel–concrete composite floor systems with profiled decking as permanent formwork in grain elevator towers, highlighting their effectiveness in minimizing resonance effects. The research presents an original configuration that enhances structural performance and operational safety, laying the groundwork for further optimization of slab parameters in future investigations. Practical significance. The results of this research can be used to improve the design of grain elevator tower floors by selecting appropriate composite configurations. The tested systems showed better vibration damping and structural stability, which contributes to safer and more reliable operation of grain cleaning equipment. These findings support engineers in making informed decisions when designing dynamically loaded agricultural facilities.

The hypothesis of using post-tensioning techniques in strengthening in situ steel trusses built compositely with high performance concrete decks is examined and evaluated experimentally and theoretically. In realizing the proposed technique, unbonded high-strength tendons are prestressed externally to provide axial compression to counteract tensile stresses caused by external loading. The effects of post-tensioning on composite truss systems are investigated as related to flexural strength and behavior. The analytical portion of the research utilizes a technique which incorporates the concepts of transformed section, principle of virtual work, and principle of superposition. In the experimental portion of the study, two full size truss specimens were simply supported at their ends and subjected to third-point monotonically increasing loads. Experimental parameters included the level of post-tensioning as applied to a complete composite system and a nominally identical truss only, without a concrete slab. Test results indicated that for the extra partial prestressing ratio (PPR) of 6.12%, the post-tensioned composite truss resisted a maximum total load 20.4% higher than that in the case of a composite truss without prestressing. The failure mode of the posttensioned composite truss occurred by yielding of the bottom chord while the tendon was still within the elastic range. This behavior resulted in a ductile failure mode displaying detectable warning deformation and is therefore preferred to sudden failure occurring without any noticeable ductile deformations. Good agreement between experimental and theoretical results was attained. The successfully developed and verified mathematical model is capable of evaluating the strength and stability of in situ structures similar to the type studied herein. The model can also be used to establish the maximum amount of post-tensioning required for structural rehabilitation as well as to evaluate the associated serviceability, and ductility factors. Such information can then be used for upgrading existing composite spans such as may be found in bridges or buildings and thereby to upgrade the flexural capacity of such linear structures by taking advantage of the high strength tendons.

Steel trusses acting compositely with concrete slabs on wide rib profile steel deck have proven to be an economical system for long span floors. The flexural behaviour of two composite trusses with a span of 11.5 m was studied. The truss configuration consisted of hollow structural section chords with double angle web members welded on either side. The flexural tests showed that ductile behaviour up to failure can be obtained without failure of the web members, provided that the design is based on the ultimate tensile strength of the bottom chord, and the web members and shear connection are designed for the concomitant forces. The maximum moments attained were about 1.2 times the unfactored ultimate moment predicted by CSA Standard S16.1. The maximum strain in the bottom chord of both trusses was significantly higher than the yield strain, but did not reach the ultimate strain due to premature shear connection failure. The failure mode of the first composite truss demonstrated the need for additional rules for establishing the length of stud shear connectors for use in slabs on ribbed deck, as has been incorporated in S16.1-M89. A design procedure for double angle web members was developed, based on the test results. Key words: behaviour, composite steel–concrete trusses, flexure, long span, ultimate moment resistance.

The significance of this study initiates from the need to produce a selection guidance on the span range, span-to-depth ratio and scheme of the composite floor truss system to provide optimum performance and cost effectiveness for a particular application area. With this objective a parametric study was designed, based on three parallel chord trusses (Pratt, Howe, and Warren) using Rectangular Hollow Structural Shapes, a constant panel size of 2.5 m, four composite floor European-profiles and a range of load intensities. Hence, the span-to-depth ratios, R S/D , and dead-to-live load ratios, R DL/LL , were ranged from 3 to 27 and 0.84 to 3.22, respectively, for each truss type. The optimization was performed by using the design results of RFEM (2018) software for approximately 675 composite floor trusses with the objective of selecting optimal depth for each truss model. In addition, this paper attempts to introduce a cost function by considering the material, fabrication and painting costs and comparative figures allowing the design to be tailored with a focus on cost reduction. Accordingly, for all truss types, span-to-depth ratio of 9 to 12 with a span range of 7 to 23 m provides the most cost effective solution. Structural steel and the welding process are the two parameters that are found to have the highest impact on total cost.

Composite floor systems—A mature design option

<p>Nowadays, the reuse and recycling of steel-concrete composite structures is a topic of significant interest. However, traditional systems do not provide easy dismantling possibilities making reuse and recycling not viable. Innovative projects like the LWT-FLOOR project ongoing at the University of Zagreb, Faculty of Civil Engineering, Croatia, are trying to overcome these obstacles. The LWT- FLOOR project aims to develop a novel structural floor system with a demountable shear connection. The proposed system is formed of built-up cold-formed steel beams and cast-in-place concrete slabs that are interconnected using an innovative demountable type of shear connection allowing the floor system components to be easily dismantled. This paper summarises an overview of the LWT-FLOOR project background and objectives, realised and planned activities with a summary of analytical, numerical and experimental results on the components and system capacity.</p>

Effective width of timber-concrete composite beams with crossed inclined coach screw connections at the serviceability state

The paper presents the cost optimization of composite floor trusses composed from a reinforced concrete slab of constant depth and steel trusses consisting of hot rolled channel sections. The optimization was performed by the nonlinear programming approach, NLP. Accordingly, a NLP optimization model for composite floor trusses was developed. An accurate objective function of the manufacturing material, power and labour costs was proposed to be defined for the optimization. Alongside the costs, the objective function also considers the fabrication times, and the electrical power and material consumption. Composite trusses were optimized according to Eurocode 4 for the conditions of both the ultimate and the serviceability limit states. A numerical example of the optimization of the composite truss system presented at the end of the paper demonstrates the applicability of the proposed approach.

Floor vibration serviceability is a primary design consideration for steel framed composite floors. The accuracy of any floor vibration evaluation procedure depends on a reasonably accurate prediction of modal properties. To consider multiple modes, a procedure must also accurately predict the spacing of modal frequencies. The goal of this paper is to investigate the ability of current finite element modeling techniques to accurately predict these modal properties. A composite floor slab was vibration tested to determine its natural frequencies, mode shapes, and accelerance frequency response functions. Analytical predictions were made using a commercially available finite element modeling program. The measured and predicted properties are compared to assess the accuracy of the modeling techniques.

A novel composite floor consisting of an upper chord of a grouted square steel tube truss and a lower chord of a reinforced concrete slab is proposed to address existing problems with precast composite floors, such as a complex construction process, high cost, significant resource consumption, and severe environmental pollution. Sixteen-point loading tests were carried out on five simply supported one-way slabs to simulate the stress state of the floor under a uniform load and to investigate the stiffness, cracking moment, load-carrying capacity, and failure mode of the composite floor system. The results showed that the composite floor system exhibited ductile failure, with cracks uniformly distributed at the bottom of the slab; additionally, the grouted steel tube did not experience uplift or out-of-plane buckling, and the truss welds did not fracture, indicating that the composite floor system still had further deformation capacity and load-carrying capacity with satisfactory stress conditions. After unloading, the residual deformation of the composite floor accounted for 28% to 36% of the maximum deflection, demonstrating good deformation recovery ability. The bottom slab thickness and truss height are key parameters that influence the new composite floor, and increasing the two parameters enhances the cracking load, deformation resistance, and flexural capacity of the composite floor, with a significant improvement achieved by increasing the truss height. The floor slab should have a minimum thickness of 60 mm, as required by China’s Code for Design of Concrete Structures, and the truss height-to-span ratio should be 1:30, which meets the deformation and load-carrying requirements of the floor and conforms to the design concept of green buildings.

This specification and supporting commentary cover the design of simply supported composite joists and trusses used in one-way floor systems. Basic design procedures are based on achieving nominal flexural strength before shear failure or local instability occur. The specification considers strength, serviceability, and construction criteria. A design example is included.

This study aims to present a multi-criteria decision analysis (MCDA) for comprehensive performance evaluation of the alternative design of timber–concrete composite (TCC) floor system. Considered objectives are serviceability and sustainability performance with associated criterion as (1) comfort class regarding springiness and vibrations, (2) architectural quality with associated criterion as open spaces, (3) environmental aspect with associated criterion as CO2 emissions and (4) cost aspect with associated criterion as the total costs. Analytical Hierarchy Process (AHP) and Complex Proportional Assessment (COPRAS) as the methods in the multi-criteria analysis have been combined for (1) determining the weighting of criteria based on the survey results, (2) verifying the consistency ratio of decision matrix made by experts and (3) for ranking and selecting the optimal concept design among design candidates. According to the results, the TCC floor with the span length of 7.3 m belonging to comfort class A has got the highest ranking. However, sensitivity analysis indicates that the TCC floor with a 9.0 m span length belonging to comfort class A shall be selected as the optimal concept design. The study contributes by developing a complete concept design tool for TCC floor systems using AHP combined COPRAS methods to handle both beneficial and non-beneficial criteria.

Glulam-concrete composite floor (GCC) is a hybrid flooring system which adopted from timber-concrete (TCC) flooring system concrete by replacing the sawn timber joist to Glulam timber joist. The concrete topping was poured on the concrete topping with stiffness connectors were installed to prevent the slip behaviour. Glulam timber is engineered timber that has a bigger strength compared to swan timber. This study is aims to identify the vibration behaviour of 7.6 m × 4.05 m Glulam Concrete Composite (GCC) floor. The walking tests were performed to get the vibration excitation on the floor. The person was walked horizontal and diagonal from one edge to another edge of the floor. The vibration data was recorded by accelerometer and analysis using ARTeMIS software package. The first natural frequency that obtained from both walking tests, (horizontally and diagonally walking test) were 12.9 Hz and 12.39 Hz, respectively. The natural frequencies were higher that 8 Hz as recommended by Eurocode 5, as acceptable value of limitation of vibration serviceability on the flooring system. As conclusion, the vibration behaviour of GCC floor was acceptable and the floor is comfortable to be used.

Effect of fire on composite long span truss floor systems