Composite Joists Research Articles

A Study on the Behavior of Composite Concrete and Open Web Steel Joists

In this research, the results of three composite open web steel joist static tests are presented along with the results of companion pushout tests. The effect of shear connection degree and span-to-depth ratio on the behavior of composite open web joists under distributed static loading is reviewed and discussed, followed by a comparison of results of the shear stud strength from push-out tests, back-calculated from the ultimate capacity of the composite joist tests, and to the provisions in the AISC, EC4, NZS, SJI, and BS5950. Specimen test results of the studied span-to-depth ratios showed that the load-deflection behavior was similar to ultimate capacity difference less than 10%, but they experienced different failure modes and deflection. And when the test results were compared based on the shear connection degree, they revealed that the composite open web joist designed with partial shear connection suffered from severe deformation and deflection accompanied with higher ultimate capacity

Flexural behavior of composite open web steel joist and concrete slab

Experimental research has been carried out to study the behavior of composite open web steel joists under monotonic loading. Four composite joists were fabricated with two types of web members and span-to-depth ratios were tested. The concrete slab 400 mm wide, and 90 mm overall depth overlaid on a corrugated steel sheet. The composite system was simply supported over 3000 mm span and subjected to a uniformly distributed loading. Test results are presented in terms of slip between composite slab and the top chord of steel joist, load-deflection and load-strain relations. Based on the experimental results, it can be concluded that lowering span/depth ratio has a significant effect on failure pattern with increase in ultimate capacity about 8%. Additionally, the results show that using double angles web type has only a little influence on deflection but increased ultimate capacity about 10% over similar composite joist with rounded bars web.

Design and behavior of light composite steel–concrete trusses with drilled standoff screw shear connections

Composite steel–concrete flexural members have become increasingly popular in the design and construction of floor systems, structural frames, and bridges. A subtype of such composite floors is a system featuring composite trusses, also referred to as composite open-web joists, which can span large lengths and provide open web space for the installation of typical utility conduits. One problem that arises with respect to composite joists has been the installation of welded shear studs. In many composite trusses, the composite action can significantly reduce the required size and thickness of the top chord. The thinner the top chord member becomes, the more difficult it is to weld studs without burning through the base member. Likewise, as the joists get smaller, the greater the sweep (lateral out-of-straightness) tends to become. For these reasons, a form of shear connector other than welded shear studs is of interest. The results of the elemental push-out tests, analytical study and the resulting strength prediction models for the strength of the shear connection have previously been presented by the authors. This paper presents the analytical and experimental findings pertaining to the design and behavior of composite truss members with standoff screws as shear connectors.

A Parametric Evaluation of Multi-Webbed Composite Joists Based on EC5

The introduction of engineered beams offers long span, low cost and light weight joists in comparison to traditional solid timber sections. However, the vibration criteria in the design codes may significantly reduce the permissible span of the joists for domestic construction. This paper investigates the influence of geometric and material variability on permissible spans of a series of multi-webbed composite joists, which are designed in accordance with the requirements of Eurocode 5 and its UK National Annex. Geometric variability comprises four different profiles, namely; I-beams, Double I-beams, Box beams and Box I-beams/joists. The variations between the profiles are web-flange connection details and the number of webs, which vary from one to three depending on the profile. Material variability involves two different web materials, OSB and plywood, which are considered together with two different flange materials, C16 and C24. This study shows that serviceability would in general govern design requirements in UK timber flooring systems. Out of four different sub-criteria defined under the serviceability conditions, the deflection under unit point load is the governing condition in most cases. It was found that the correct choice of materials and beam profile can enhance the permissible span by up to 34%. When lateral restraint is not provided, lateral stability becomes the controlling criterion as beam depth increases. An inverse relationship has been found between the permissible span and the beam depth for an I-beam profile, whereas for the Double I-beams a constant permissible span was observed for varied beam depths. For the Box beams and Boxed I-beams, the permissible span will increase in proportion to beam depth. This study also shows that the effect of lateral stability on solid timber joists is less pronounced than for engineered beams.

Drilled standoff screws for shear connection in light composite steel–concrete trusses

Composite steel–concrete flexural members have become increasingly popular in the design and construction of floor systems, structural frames and bridges. A particularly popular system features composite trusses (open web joists) that can span large lengths and provide open web space for installation of typical utility conduits. One problem that arises with respect to composite joists has been the installation of welded shear studs. As the joist span gets smaller, the top chord also gets smaller. The thinner the top chord member becomes, the more difficult it is to weld studs without burning through the base member. Likewise, as the joists get smaller, the greater the sweep (lateral out-of-straightness) tends to become. For these reasons, a form of shear connector other than welded shear studs is of interest. This paper presents research results for a new type of shear connector, the standoff screw. This type of connector is drilled, rather then welded, and represents a viable alternative to headed shear studs in light composite trusses or open web joists. Results of experimental and analytical research are presented, as well as the development of a recommended design methodology.

Increasing the flexural performance of RC beams strengthened with CFRP materials

In recent years scientific attention has focused on the use of FRP composites as the most promising technologies for repairing, strengthening or retrofitting existing structures to resist higher loads and to rectify damage. The use of external FRP as flexural strengthening gives advantages in terms of resistance, stiffness and ductility. In this paper, a new methodology of reinforcement is applied on a beam in order to increase its load carrying capacity, by generating a higher internal couple of the transversal section, but leaving the weight of the element practically the same. This was possible by using a new composite joist, joined at the intrados of the original beam. The study was carried out on beam samples scaled 1:2 size. The results obtained show that this methodology was very useful in the case of a transformation of the use of a civil structure and also when an increase of the resistant section is required.

Composite Steel Joists

Composite steel construction has been recognized for a number of years as one of the most economical systems for constructing building floors. Three options have evolved over the years to meet the requirements for building height limitations and the need to run complex heating, ventilating, electrical, and communication systems: (1) Composite wide flange beams with web openings; (2) Stub girders; and (3) Open web steel joists and joist girders. This paper focuses on the advantages associated with composite open web steel joists, development and testing of open web steel joists, behavior of welded shear studs observed while testing composite joists, case histories of projects using composite joists, unique vibration considerations associated with joist floors, and current status of composite joist specification development.

Proposed Specification and Commentary for Composite Joists and Composite Trusses

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.

Composite Open-Web Steel Joists

This report presents a description of research on the behavior of composite joists. In this type of structure a concrete slab is connected by shear-connectors to a steeljoist. The research to be described consists of tests on beams. The purpose of the research was to determine the behavior of the shear-connectors.