Takeo Hirashima

Fire performance, including the cooling phase, of structural glued laminated timber beams

Purpose Based on heating tests and load-bearing fire tests, this paper aims to discuss the charring rate, the temperature distribution in the section and the load-bearing capacity of structural glued laminated timber beams not only during the heating phase during a 1-h standard fire in accordance with ISO 834-1 but also during the cooling phase. Design/methodology/approach Heating tests were carried out to confirm the charring rate and the temperature distribution in the cross-section of the beams. Loading tests under fire conditions were carried out to obtain the load-deformation behavior (i.e. the stiffness, maximum load and ductility) of the beam. Findings The temperature at the centroid reached approximately 30°C after 1 h and then increased gradually until reaching 110-200°C after 4 h, during the cooling phase. The maximum load of the specimen exposed to a 1-h standard fire was reduced to approximately 30 per cent of that of the specimen at ambient temperature. The maximum load of the specimen exposed to a 1-h standard fire and 3 h of natural cooling in the furnace was reduced to approximately 14 per cent. In case of taking into consideration of the strength reduction at elevated temperature, the reduction ratio of the calculated bending resistance agreed with that of the test results during not only heating phase but also cooling phase. Originality/value The results of this study state that it is possible to study on strength reduction in cooling phase for end of heating, timber structural which has not been clarified. It is believed that it is possible to appropriately evaluate the fire performance, including the cooling phase of the timber structural.

Load-bearing Capacity of H-shaped Steel Columns under Local Buckling at Elevated Temperature

When a compartment fire occurs in a building of steel structure, large bending deformations are produced at the ends of columns and beams, inducing local buckling at these points. In this study, the load-bearing capacity of H-shaped steel columns under local buckling is clarified from pure compression tests and bending compression tests at constant temperatures ranging from room temperature to 600°C. On the basis of the tests, we propose, in relation to the fire resistance of H-shape steel stub columns, a relation between safety usable steel temperature and constant axial load ratio.

Deflection behavior and load-bearing period of structural glued laminated timber beams in fire including cooling phase

Purpose This paper aims to discuss the fire performance of glulam timber beams based on their deflection behavior and load-bearing period, which were obtained from load-bearing fire tests under constant load conditions. Design/methodology/approach In this report, the fire performance, primarily deflection behavior and load-bearing period of glued laminated (glulam) timber beams will be discussed from the standpoint of load-bearing fire tests conducted during the cooling phase under constant load conditions. Then, based on the charring depth and the per section temperature transformation obtained from loading test results, the load-bearing capacity of the glulam timber beams will be discussed using the effective section method and the strength reduction factor, which will be calculated in accordance with the European standards for the design of timber structures (Eurocode 5). Findings In the cooling phase, the charring rate is decreases. However, as the temperature in the cross section rises, the deflection is increases. The failure mode was bending failure because of tensile failure of the lamina at the bottom of the beam. Moreover, a gap caused by shear failure in a growth ring in the beam cross-section in the vicinity of the centroid axis was observed. Shear failure was observed up until 1 to 3 h before end of heating. The calculated shear strength far exceeded the test results. Shear strength for elevated temperature of glued laminated timber is likely to decrease than the shear strength in Eurocode 5. Originality/value Unlike other elements, a characteristic problem of timber elements is that their load-bearing capacity decreases as they are consumed in a fire, and their bearing capacities may continue to degrade even after the fuel in the room has been exhausted. Therefore, the structural fire performance of timber elements should be clarified during not only the heating phase but also the subsequent cooling phase. However, there are few reports on the load-bearing capacity of timber elements that take the cooling phase after a fire into consideration.

Tensile Resistance of Splice Connections with High-Strength Bolts in Fire

This paper presents the results of two high-temperature tensile tests (steady-state tests and transient-state tests) of splice connections with high-strength bolts. First, steady-state tensile tests at high temperature were conducted to obtain the load-deformation behavior and tensile resistance of the connections. The tensile test results indicated that the ductility of connections increased when the steel temperature was over 500 °C. Second, transient-state tensile tests at constant load and increased temperature were conducted to investigate the influence of deformation rate on resistance. In the transient-state tests, the specimens were subjected to a constant load that was the maximum load from the steady-state test or from the calculated tensile resistance based on AIJ recommendations. In the ultimate stage under the transient state, the deformation rate for the connection considerably increased and contributed to improved resistance at elevated temperature. On the basis of these experimental results, this paper discusses the tensile resistance of splice connections with high-strength bolts exposed to fire.

Influence of Water Content on Total Strain of Super High-Strength Concrete Under Elevated Temperature

The purpose of the present study is to present an accurate constitutive model of the concrete under elevated temperature. The present study is an experimental study on the influence of evaporable water in concrete, the water/binder (W/B) ratio, and the loading level on the thermal strain and the total strain of high-strength concrete up to 700 °C. The cylindrical specimens were preconditioned by air-drying or oven-drying at 105 °C. Expansion was larger for total strains in oven-dried specimens than those in air-dried specimens between 100 and 500 °C at stress levels from 0 to 30 %. The influence of W/B ratio was unclear. The coefficient of load-induced thermal strain (LITS), a measure of strain identified by subtracting the thermal strain from the total strain, and thermal expansion coefficient were higher for oven-dried specimens than for air-dried specimens below 200 °C. When the stress level was increased, the differences for both were more evident. The formularization of the total strain was performed in accordance with LITS model. The calculated values indicated reasonable agreement with the experimental values relatively for air-dried specimens at load levels of 30 % and 50 %.

DEFLECTION BEHAVIOUR AND LOAD BEARING CAPACITY OF LARCH GLUED LAMINATED TIMBER BEAMS EXPOSED TO STANDARD FIRE HEATING DURING THE COOLING PHASE: Study on fire performance of structural glued laminated timber beams Part 2@@@構造用集成材梁の耐火性に関する研究 その2

Timber elements, which are different from other structural elements, have a characteristic problem in that the load bearing capacity decreases due to self-burning in the case of a fire, and this self-burning may continue after other fuel in the room has been exhausted. Therefore, the structural fire performance of timber elements should be clarified during not only the heating phase, but also the cooling phase. In the present paper, deflection behaviour and failure mode of larch glued laminated timber beams exposed to fire heating and natural cooling is discussed based on load-bearing fire tests in which load level is the test parameter.

Study on Bending Strength of Web-Bolted Moment Joints of Aluminum Alloy Beam Exposed to Fire

This study narrows the application temperature field of aluminum alloy to 350 °C or less, and examines the strength of web-bolted moment joints within that temperature range. Bending strength of web-bolted moment joints of aluminum alloy exposed to fire is investigated experimentally and analytically. It is observed that if splice plate length and the beam section are designed appropriately, it is possible that maximum bending strength is fully realized with the web-bolted moment joints. The transmission mechanism of the bending moments is thought to be based on prying action between the flanges and splice plate side edge. The effect of prying action contributes to the maximum bending strength. Maximum bending strength ratio is 90–60 %.