| Mountain architecture is widely used because of its unique structural form and good terrain adaptability.As one of the most common forms of mountain building structures,the stilted frame structure has the inevitable unequal height grounding column,and the horizontal and vertical stiffness distribution is seriously uneven,making the structure’s force different from ordinary frame structure and torsion effect Significantly.In this paper,a number of three-dimensional models of mountain stilted frame structures have been established through SAP2000 and PKPM software,and the influence of the stilted slope,aspect ratio,span number,floor eccentricity and special components on the stilted structure has been investigated.Analyzing the law of torsion effect of the stilted structure and the weak parts of torsion,the definition index and scope of the two-way ground motion input of the stilted structure are proposed,and the torsion resistance method of the stilted structure of the mountain is researched and relevant design suggestions are given.The main conclusions obtained in this paper are as follows:1)Ordinary frame structure receives uniform force under the action of earthquake.However,due to the difference in stiffness distribution of the stilted frame structure,the stiffness contribution rate of short column easily reaches more than 80%,resulting in serious uneven distribution of force on the first layer of the structure.The force is concentrated in the short post.Secondly,the pillars on both sides of the first floor of the stilted will produce a large axial force,and the impact on the structure cannot be ignored;2)The cross-slope torsion effect of the stilted structure is inevitable under the action of earthquake,and it increases with the increase of the structure slope,aspect ratio,and the number of spans along the slope.The torsion effect of the first floor of the structure is compared with other floors more significant.Under the action of rare earthquakes,the first hinged part of the stilted structure is always located at the suspension foot short column,and it exists in the form of a beam and column mixed hinge,and the yield of the plastic hinge is large.Taking the short column on the first floor as the center,the surrounding beams and column members are seriously damaged,and some have lost the bearing capacity(section C～D),causing the partial collapse of the upper floor.The long stilted column is basically elastic and has not entered plasticity.Satisfy the design requirements of "not falling in a big earthquake".Although the torsion displacement ratio can reflect the torsion effect of the stilted structure,its size needs to be appropriately increased or canceled the control of the displacement ratio limit;3)The shear force increase coefficient can well reflect the relationship between the structural torsion effect and the bidirectional ground motion input.The shear force increase coefficient of the short column and the floor increases with the increase of the eccentricity.When the eccentricity of the first floor of the stilted structure exceeds 15%,the two-way ground motion input should be considered;4)The design suggestions for the stilted frame structure are as follows:(1)The slope of the stilted site should not be greater than 40 degrees;(2)The short column should be increased by one level of seismic resistance or multiplied by a reinforcement increase factor greater than 1;the short column should extend to the bottom of the foundation or should not be short.As far as possible,the rigidity of the stilted leg shall be distributed as evenly as possible;(3)The method of setting tension beams,steel supports and shear walls around the flexible edge of the first layer of the stilted leg reduces the calculated length of the long column and improves the lateral rigidity of the sling leg;(4)The rigidity of the hanging leg part is required to be no less than the rigidity of the adjacent upper floor to avoid the formation of a weak layer due to sudden changes in structural rigidity. |
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