1,721,002 research outputs found
The design of a semi-prefabricated LVL-concrete composite floor
No full textThis paper describes the design of a novel semi-prefabricated LVL-concrete composite floor that has been developed in New Zealand. In this solution, the floor units made from LVL joists and plywood are prefabricated in the factory and transported to the building site. The units are then lifted onto the supports and connected to the main frames of the building and to the adjacent units. Finally, a concrete topping is poured on top of the units in order to form a continuous slab connecting all the units. Rectangular notches cut from the LVL joists and reinforced with coach screws provide the composite action between the concrete slab and the LVL joists. This system proved to be an effective modular solution that ensures rapid construction. A design procedure based on the use of the effective flexural stiffness method, also known as the ‘gamma method’ in accordance with the Annex B of Eurocode 5, is proposed for the design of the composite floor at ultimate and serviceability limit states, in the short- and long-term. By comparison with the experimental results, it is shown that the proposed method leads to conservative design. A step by step design worked example of this novel semi-prefabricated composite floor concludes the paper
“Fatigue behaviour of timber-concrete composite connections and floor beams.”
No full textIn recent years, timber–concrete composite systems have become more widely used as a new construction technique for buildings and bridges. The main advantage is that the compressive strength of concrete is exploited through the use of composite action while timber beams are able to resist the tensile stresses. The level of composite action, which can be achieved by the system, is dependent on the type of shear connector used. There is a lack of knowledge, however, on the performance of these types of connections
when subjected to cyclic loading, which is typical for bridges. Testing was performed in the Structures
Laboratory of the University of Canterbury to analyse the fatigue behaviour of two types of timber–concrete
connections via push-out specimens, and two beam specimens representing strips of composite floor with the same connection types. The two types of connection investigated were: (i) a rectangular notch connection reinforced with a coach screw (also known as lag screw); and (ii) a connection with
toothed metal plates punched into laminated veneer lumber (LVL). The stiffness of the connection was monitored throughout the cyclic loading along with the total amount of slip occurring between the concrete and timber. After the application of 2 million cycles, the push-out and beam specimens were loaded to failure in order to quantify their maximum strength. The strength of the rectangular notched connection after cyclic loading was 0.95 times of the one without cyclic loading, while for the metal plate connection was 0.60 times. For the metal plate connection, a continuous increase in slip was observed with increased cycles possibly due to accumulated damage from repeated loading. The rectangular notch connection displayed more resistance to changes in slip, strength and stiffness than the metal plate connection. No obvious loss of stiffness was observed in the rectangular notch connected floor beams after
2 million cycles, and when tested to failure the stiffness was very similar to the same floor beam that had not been cyclically loaded. The floor beam with metal plate connections did not perform well and failed after 350,000 cycles. The loss of strength, stiffness and composite action in this floor beam compared to the one without cyclic loading was significant. In this respect, the rectangular notch connection system is recommended for use in bridge design as opposed to metal plate connections
"Long-term performance of LVL-concrete composite beams under service load"
No full textThe long-term behaviour of timber-concrete composite is characterized by the response of its three components (timber, concrete and connection) to load, moisture content, temperature and relative humidity of the
environment. This paper reports results of a 4-years long-term test on three 8m span laminated veneer lumber (LVL)-concrete composite floor beams under service load performed in an indoor, uncontrolled, and unheated environment at the University of Canterbury. The environmental conditions were characterized by either low temperature with high
relative humidity or high temperature with low relative humidity, conditions considered to be reasonably severe and presumably close to service class 3 according to Eurocode 5. The mid-span deflections were extrapolated to the end of service life (50 years) and compared to span/200 deflection limit, which was exceeded by all beams
“Experimental behaviour of LVL-concrete composite floor beams at strength limit state.”
No full textThis paper reports the outcomes of short-term collapse tests performed on eleven laminated veneer lumber (LVL)–concrete composite floor T-beams. Different variables such as span length (8 and 10 m), connection and concrete types, and design level (well- and under-designed, in terms of connector numbers) were investigated. During 4-point bending tests, mid-span deflection, connection slips and strains were measured. Connection types investigated include triangular and rectangular (150 mm and 300 mm long) notches cut in the timber and reinforced with a coach screw, and modified toothed metal plates pressed on the edge of the LVL joists. All of the beam specimens were designed using the effective bending stiffness or γ -method, in accordance with Annex B of Eurocode 5. The same method was used for an analytical–experimental comparison of the beam’s performance at ultimate (ULS) and serviceability (SLS) limit state.
All well-designed beams provided more than 95% composite action even though there were relatively few connectors (e.g. six 300 mm long notches on the 8 m span beam). The ULS and SLS live load capacity of the beams was found to be approximately 90% of that of a fully composite beam. Correction factors providing a 15% increase for deflection and a 13% reduction of the effective bending stiffness are proposed for calculations using the transformed section method for all well-designed beams, i.e. beams designed using the γ -method according to Annex B of Eurocode 5. Although the γ -method was found to be significantly underestimate the ULS strength, it provided an accurate prediction of the short-term deflection. In terms of the connection type, the 300 mm rectangular notches provided the best performance, with high stiffness and strength beyond the ULS load level, and requiring fewer connectors along the beam. The triangular notch was found to be a viable alternative, with more connectors but was easier and faster to cut than a rectangular notch. Metal plate connectors provide a practical construction possibility, but the beam stiffness was found to rapidly deteriorate beyond the ULS load level
"Long-term performance of LVL-concrete composite beams under service load"
No full textThe long-term behaviour of timber-concrete composite is characterized by the response of its three components (timber, concrete and connection) to load, moisture content, temperature and relative humidity of the
environment. This paper reports results of a 4-years long-term test on three 8m span laminated veneer lumber (LVL)-concrete composite floor beams under service load performed in an indoor, uncontrolled, and unheated environment at the University of Canterbury. The environmental conditions were characterized by either low temperature with high
relative humidity or high temperature with low relative humidity, conditions considered to be reasonably severe and presumably close to service class 3 according to Eurocode 5. The mid-span deflections were extrapolated to the end of service life (50 years) and compared to span/200 deflection limit, which was exceeded by all beams
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