The Wind Uplift Failure Mechanism And Wind Vulnerability Analysis Of Standing Seam Metal Roof Plate

Metal roof plate is widely used as the cladding of large-span roof because of its light weight and simple construction.But in recent years,wind disasters of metal roof plate have occurred frequently.Previous studies have shown that the wind uplift failure modes of metal roof plates mainly include static failure and fatigue failure.Static failure refers to the strength failure of roof plates caused by the peak wind load in normal wind,while fatigue failure refers to the low cycle fatigue failure of roof plates caused by the fluctuating wind load with high amplitude in extreme wind.Throughout the current wind-resistant design process of roof cladding,it is not difficult to find that this is a design method based on the checking calculation of the bearing capacity of roof plate unit components,which cannot provide the probability of roof plate failure.In particular,the strength of the connection between components needs to be checked by wind-resistant test,which increases the design cost.In order to make up for the shortcomings of the current windresistant design,this paper carries out the wind vulnerability analysis considering the failure mode of the roof plate.The vulnerability curve can provide the probability of the roof plate reaching all performance levels.Based on the research of this paper,after determining the wind load of roof partition,the performance-based wind-resistant design can be further carried out in combination with the performance target of owner.At present,the following problems still exist in the vulnerability analysis of roof plate.Firstly,the existing research on wind-resistant performance pays more attention to the limit state of roof plate and less attention to the wind uplift failure process,which leads to the unclear wind uplift failure mechanism;Secondly,the load cycle used in the dynamic wind-resistant test considering fatigue damage is conservative,which leads to high simulation cost.In order to carry out vulnerability analysis,it is urgent to establish a simplified numerical analysis method for the fatigue failure of roof plates;Finally,most of the existing studies on the performance level of roof plate are aimed at the whole roof cladding,and there is a lack of research on the performance level of roof plate units.Therefore,in order to carry out wind vulnerability analysis,this paper has carried out the following work:(1)The wind uplift failure mechanism of roof plate under static failure is revealed.Based on static test and numerical simulation,the static wind uplift failure process of roof plate is studied.Both the occlusion failure and tearing failure followed the characteristics of three stages,that is,the development of materials from elasticity to plastic platform and then to plastic development.The occurrence of two kinds of failure mode resulted from the difference of the stiffness ratio between anti-wind clip and roof plate in the process of plastic development.Therefore,the failure parameter η considering the impact of stiffness ratio is established to evaluate the damage degree of roof plates,and the failure criterion of roof plate is determined as the failure parameter η reaches 1.0.(2)The third-stage performance level of roof plate units is quantified based on the failure parameter η in static simulation cases,and the failure parameter η is0.4,0.7 and 1.0 when the roof plate reached moderate damage,severe damage and failure,respectively.7000 calculation samples are obtained by Latin hypercube sampling,and the wind vulnerability analysis of 14 commonly used type of standing seam metal roof plate is carried out.The research shows that reducing the plate width will increase the stiffness of the roof plate,and then improve the wind-resistant performance of the roof plate.Every 0.1m reduction in the plate width can increase the corresponding load by 0.5～1.5 k Pa under the same performance state.The addition of anti-wind clip and the reduction of support spacing are equivalent to increase the occlusal strength of roof plate,and will also improve the corresponding load under the same performance state to varying degrees.Based on the vulnerability curve of roof plate under static failure,the feasibility of performance-based wind-resistant design is verified by comparing the application of performance-based wind-resistant design and traditional windresistant design in static failure.Performance-based wind-resistant design can realize the economy of wind-resistant design by providing a variety selection of roof plate models.(3)A simplified numerical analysis method for fatigue failure considering material damage is proposed.The damage constitutive model of 3004-H24 AlMg-Mn roof plate material is established based on the cyclic loading test and numerical simulation.Through the time history analysis considering the damage constitutive,it is found that only the load sequence with the maximum load ratio and load ratio amplitude greater than 0.7 will cause damage to the material.Then based on the principle of damage variable equivalent,the simplified load sequence is proposed to reduce cost simulation.(4)Based on dynamic test and simplified numerical analysis method,the fatigue failure mechanism of roof plate is studied.The research shows that the fatigue failure mainly occurs in the cases with anti-wind clip.The reciprocating interaction between roof plate and anti-wind clip under cyclic load makes the material damage of roof plate obvious,resulting in the tearing failure of roof plate under dynamic loading.The failure process meets the three-stage characteristics of the material from no damage to obvious damage of individual elements,and then to the simultaneous failure of adjacent elements due to damage.The three stages correspond to different damage accumulation degrees,which can be evaluated by damage variable D.Therefore,damage variable D reaching 1.0 is taken as the fatigue failure criterion of roof plates.(5)Based on the statistical results of damage variable D in dynamic simulation cases,the damage variables D is 0.2,0.6 and 1.0 respectively when the roof plate reaches moderate damage,serious damage and failure under fatigue failure.Because the fatigue failure only occurs in the case with anti-wind clip,5000 calculation samples are obtained through Latin hypercube sampling,and the wind vulnerability analysis is carried out on 5 commonly used type of roof plates.The results show that the cumulative damage of materials accelerates the damage process of roof plates,and the vulnerability of roof plates under fatigue failure is inferior to that under static failure.Furthermore,based on the vulnerability curve of roof plate under fatigue failure,the application of performance-based windresistant design in fatigue failure and static failure is analyzed and compared.