130,401 research outputs found
“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
"Design of reinforcement around holes in laminated veneer lumber (LVL) beams"
No full textMany practical situations require holes in timber beams. When the hole is large relative to the depth, the failure of the beam is governed by crack initiation and propagation around the hole. Cracking of a timber beam decreases the capacity
of the beam considerably. This paper presents a method for designing the reinforcement around holes in Laminated Veneer Lumber (LVL) beams so as to recover their full flexural capacity. The design procedure is complemented by two worked examples where all verifications are discussed in detail
"Design of timber-concrete composite floors for fire resistance"
No full textThis research investigated the fire performance and failure behaviour of timber-concrete composite floor systems currently under development in New Zealand,
resulting in a calculation method for evaluating the fire resistance of these floors. Furnace tests were performed on two full-size floor specimens at the Building Research Association of New Zealand (BRANZ). Both floor specimens were 4m
long and 3m wide, consisting of 65mm concrete topping on plywood formwork, connected to double LVL floor joists. They were tested over a 4m span, subjected to a nominal design live load of 2.5 kPa. Both floors were subjected to the ISO 834 test fire for over 60 minutes. Two separate connection types were tested; concrete notches cut into the timber beams with an incorporated shear key, and metal toothed plates pressed between the double beams.
It was found that the reduction in section size of the timber beams due to the fire governed the failure mode of the floors. The test data and visual observations aided in the development of an analytical model for evaluating the fire resistance of the floors. This was developed into a spreadsheet that is able to predict the expected fire resistance of these floors, taking into account some major time dependent variable properties that can have an effect on the overall performance. Load-span tables have been produced to give the estimated fire resistance of floors with differing floor dimensions, span lengths and applied loads
Effect of hole location on the load-carrying capacity of laminated veneer lumber (LVL) beams
No full textPredicting load-carrying capacity of timber beams with holes requires a model capable of accounting for the microscopic material behaviour that influences crack initiation and propagation. The complex stress distribution around the periphery of a hole causes additional tension perpendicular to grain stresses which can change the failure mode of the beam. This situation can also be affected with a change of hole location within the beam depth because stress intensity factor will be increased by tensile stresses and decreased by compressive stresses. This is not an unlikely situation as services often have to pass through beams at different depths. This paper investigates the effect of changing the hole location through the depth of Laminated Veneer Lumbers (LVL) beams utilising an experimental and numerical investigation. Experimental tests to failure of LVL beams and numerical simulations using finite element methods have shown that for a hole eccentricity of less than 20% of the beam depth, the load-carrying capacity of the beam did not change significantly. The numerical method showed that for the three-point loading condition the hole location along the beam length did not affect the failure load of beam as long as the hole was located at a distance of at least the beam depth from the supports and from the concentrated load. For uniformly distributed loading, a linearly decreasing stress intensity factor from the support to mid-span was exhibited, showing an increase in load-carrying capacity as the opening approached mid-span
“Experimental behaviour of Laminated Veneer Lumber (LVL) beams with holes and different methods of reinforcement.”
No full textHoles in timber beams used as part of a floor system within a building are often required to allow services (such as electrical and plumbing) to pass through the beams. Cutting holes can initiate cracks that can propagate when beams are loaded, mostly because of low tension strength perpendicular to grain of timber. Crack propagation changes the failure mechanism of beams, and fracture can occur at considerably lower than predicted loads. Reinforcing of timber beams to stop or prevent crack formation or propagation can be accomplished using different methods including glued in screws, fully threaded screws, plywood, and steel plates. The effectiveness of each method depends on many factors such as bonding with
the timber, the area covered (for plates or gussets), proximity to the crack surface (for crack control), and mechanisms of stress distribution and transfer.
This paper presents the results of an experimental program conducted at the University of Canterbury,
New Zealand on Laminated Veneer Lumber (LVL) beams with holes and reinforcement methods around holes. Experiments showed that opening have considerable effect on the strength reductions of LVL beams that is recoverable through reinforcing around the hole. Different sizes and shapes of openings were tested. The effectiveness of several methods of reinforcement was investigated. Experiments
showed that plywood worked most effectively for reinforcing LVL beams. Screws and glued in rods were
effective for limited the hole diameters
"Design of timber-concrete composite floors for fire resistance"
No full textThis research investigated the fire performance and failure behaviour of timber-concrete composite floor systems currently under development in New Zealand,
resulting in a calculation method for evaluating the fire resistance of these floors. Furnace tests were performed on two full-size floor specimens at the Building Research Association of New Zealand (BRANZ). Both floor specimens were 4m
long and 3m wide, consisting of 65mm concrete topping on plywood formwork, connected to double LVL floor joists. They were tested over a 4m span, subjected to a nominal design live load of 2.5 kPa. Both floors were subjected to the ISO 834 test fire for over 60 minutes. Two separate connection types were tested; concrete notches cut into the timber beams with an incorporated shear key, and metal toothed plates pressed between the double beams.
It was found that the reduction in section size of the timber beams due to the fire governed the failure mode of the floors. The test data and visual observations aided in the development of an analytical model for evaluating the fire resistance of the floors. This was developed into a spreadsheet that is able to predict the expected fire resistance of these floors, taking into account some major time dependent variable properties that can have an effect on the overall performance. Load-span tables have been produced to give the estimated fire resistance of floors with differing floor dimensions, span lengths and applied loads
Effect of hole location on the load-carrying capacity of laminated veneer lumber (LVL) beams
No full textPredicting load-carrying capacity of timber beams with holes requires a model capable of accounting for the microscopic material behaviour that influences crack initiation and propagation. The complex stress distribution around the periphery of a hole causes additional tension perpendicular to grain stresses which can change the failure mode of the beam. This situation can also be affected with a change of hole location within the beam depth because stress intensity factor will be increased by tensile stresses and decreased by compressive stresses. This is not an unlikely situation as services often have to pass through beams at different depths. This paper investigates the effect of changing the hole location through the depth of Laminated Veneer Lumbers (LVL) beams utilising an experimental and numerical investigation. Experimental tests to failure of LVL beams and numerical simulations using finite element methods have shown that for a hole eccentricity of less than 20% of the beam depth, the load-carrying capacity of the beam did not change significantly. The numerical method showed that for the three-point loading condition the hole location along the beam length did not affect the failure load of beam as long as the hole was located at a distance of at least the beam depth from the supports and from the concentrated load. For uniformly distributed loading, a linearly decreasing stress intensity factor from the support to mid-span was exhibited, showing an increase in load-carrying capacity as the opening approached mid-span
"Design of reinforcement around holes in laminated veneer lumber (LVL) beams"
No full textMany practical situations require holes in timber beams. When the hole is large relative to the depth, the failure of the beam is governed by crack initiation and propagation around the hole. Cracking of a timber beam decreases the capacity
of the beam considerably. This paper presents a method for designing the reinforcement around holes in Laminated Veneer Lumber (LVL) beams so as to recover their full flexural capacity. The design procedure is complemented by two worked examples where all verifications are discussed in detail
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