Experimental Study On Fire Resistance Of Prestressed Grid

With the rapid development of economy, people constantly proposed new standards and functional requirements of buildings. For some large buildings across the space,people proposed a higher use of functional requirements, which makes steel been widely used.And prestressing steel because of its many advantages can replace steel to improve structural performance, lower steel consumption.Prestressing steel structural is the previously applied load of prestressing steel on steel, steel structure control so opposite sign of stress and stress generated loads generated design section, forming a favorable stress distribution in the structure.Prestressed steel truss structure is the most common type of structure, embodies the perfect combination of technology and modern space prestressed steel structure, this system sets the structure and length of cable truss structure, the grid Create prestressed structural system, the perfect solution to span space structure building system requirements, not only reduces the structural internal force peak, reducing the structural deflection, but also enhance the stability of the structure, reduce the cost saving steel, this structure widely used in stadiums around the world, exhibition halls, shopping malls, terminals and other large space buildings. But these architectural features complex, large fire hazards, fire caused more casualties, and the role of mechanical properties of steel under fire degradation, tendons loose, causing damage to the load under normal use of the building structure, damage or even collapse, so the prestressing Steel truss study fire resistance is particularly important. In this paper, an integral part of the grid that is prestressed prestressed Square Pyramid started, consider the size of the vertical load and prestressed these two factors, the analysis and experimental study of fire finite element software, through theoretical analysis and real fire tests the following conclusions:1. Using finite element analysis software to correctly fire resistance of prestressed truss under load and fire coupling effect.2. In the early stages of a fire burning due to the temperature lower than the prestressing wires of the lower chord, the temperature difference between the two, the temperature of internal forces generated when heated, may become lower chord member by the pressure of the lever rod, the corresponding prestress wire tension will increase if the tension exceeds the carrying capacity of tendons may cause tendon damage. With the growth of the burning time, and prestressed steel wire rod temperature difference decreases, both affected by temperature deformation produced consistent, bars and tendons of the internal forces and restored to its original level, but as the temperature is further increased, the material properties change, the elastic modulus decreases, loosening of prestressed steel wire deformation will greatly reduce the loss of prestressing effects, internal forces will change the structure, the structure further accelerate damage.3. Obtained by thermal coupling analysis and fire tests under fire belly prestressed truss rod temperature reaches500℃～600℃, the performance of the steel material changes, a sharp decline in carrying capacity, the structure began to deform down until the sudden buckling member webs instability failure.4. Fire source has a central location on the fire resistance of prestressed truss significant influence, under fire in different parts of prestressed truss warming each case, from the fire closer to the rod warming rapidly, due to the temperature difference between the pole pieces, the temperature stress is generated, so that the internal forces of the lever is changed from the fire lever closer to the temperature to produce additional compressive force, the lever member is more prone to damage.5. Internal forces of change under fire prestressing wires penetrate the lower chord changes and internal forces and temperature changes prestressing wire on both. Under the same prestressing, the greater the vertical load components generated by the fire when the maximum vertical displacement effect is smaller, the greater the prestressing destroyed, the internal forces increased penetration of prestressing steel bottom chord smaller; vertical loads no effect on the horizontal displacement and vertical displacement of the final structure, with no effect on the rate of change of the internal forces and did not penetrate the webs of steel bottom chord. Same vertical load, the different components of prestressed prestressed displacements and internal forces did not change abdominal penetration rod and wire bottom chord is not affected by the fire when the effect of the impact of the structure in all directions; greater the prestressing, the role of the destruction by fire when compared with the initial value of the larger prestressing decreases, the penetration of the bottom chord of the prestressing steel internal forces greater than the initial value increases.