Structural Performance Of Pre-embedded-bolt Joint And Semi-rigid Single-layer Latticed Shells With Rectangular Hollow Sections

Single-layer latticed shells are widely used in free form structures because of its succinctness and transparence.For single-layer latticed shells,especially free form shells,rectangular section hollow member is a better option compared to circular section hollow member.For rectangular section is better both in mechanical behavior and structure appearance.So far,lack of excellent assembly joint with rectangular section member is one of the most important problems in single-layer shell area.Unlike circular section member,rectangular section member has a strong axis and a weak axis.Most research focused on the influence of semi-rigidity joints on single-layer shells with circular section members.This paper’s work mainly focused on two aspects:the development and study of novel assembly joints and the effect of joints’ rigidity on single-layer latticed shells.An assembly joint with pre-embedded bolts without openings was proposed in Chapter 2.The procedures of the joints’ fabricating and assembling was illustrated.Four-point bending test of 16 specimen was conducted considering the effect of bolt diameter,thickness of plate,distance between node and beam end plate and openings.The test results shows that the bending stiffness and bending capacity both descended with the decrease of bolt diameter and plate thickness and with the increase of distance between node and beam end plate.There are three failure pattern for this joint:bolts failure,end plate failure,member failure.In contrast to joints with openings,the joint proposed by author has lower bending stiffness,but better capacity and ductility.In Chapter 3 a refinement finite element model with solid element was established to simulate a static test of socket joints.With the consideration of contact effect,the simulation results coincided well the test results which proved the validity of the FE model.Bending test in Chapter 2 was simulated with the very same FE model.The load-displacement curve and load-strain curve of simulation met well with those of test in elastic stage.The fit was not quite good in elastic-plastic stage.The capacity of FE model is slightly bigger than test results.Parametric analysis of the joint was conducted with the help of FE model.The theoretical equation of initial rigidity,elastic capacity and plastic capacity of the joint under pure bending condition was proposed base on the assumption that the node and endplate were rigid.The results of equations fitted well with the simplified FE model.Static test of 8 six-member models was conducted in Chapter 4 to explore the mechanical behavior of the pre-embedded bolts joints under complex working condition.The effect of bolts dimension,distance between bolts and thickness of node was considered.The practicability of angles between node and members was also investigated.With the hollow-six-prism design of node,4° and 8° between node and members were fulfilled.The test results showed this joint was easy to fabricate and assemble and had high performance in rigidity and ductility.The initial stiffness and capacity of six-member model descended with the decrease of bolts dimension and distance between bolts.The reduce of node thickness had no effect on initial stiffness,but may weaken the capacity.In Chapter 5,the six-member model test was simulated by three different FE models which model based on solid element,model based on spring element and model based on beam element.The load-displace curves of three models all coincided well with test results in elastic stage.The solid element model had best accuracy in elastic-plastic stage.The relative error of initial stiffness of three models was smaller than 30%while the relative error of capacity was smaller than 5%.The model based on solid element could accurately simulate the mechanical behavior and stress distribution of specimen.It could be used to investigate the semi-rigidity of specific joints.Models based on spring element and beam element were less time consuming and easier to converge.For spring element model,the semi-rigidity of joints needed to be extracted to obtain the generalized load-displacement of spring element.The spring element model could be used to study the common effect of joints’ semi-rigidity on shell stability.Model based on beam element kept all the information of joint components which could reflect the influence of dimensions of different components on joints rigidity.It could be used to study the influence of specific joints on latticed shells.In Chapter 6,the relationship between relative initial stiffness β of two-member structure and joint relative rigidity κ was derived and verified.It showed,for two-member structure,the relative initial stiffness,β,was single value function of relative rigidity of joint,κ.It mean that the relative initial stiffness of two-member structure was only determined by the relative rigidity of joint.With the model based on spring element,the β-κ relationship of five different single-layer spherical domes was investigated.For each type of dome,the influence of span,rise-span ratio,number of rings and section of members was taken into account.The FE results showed the dimensions of dome had slight influence on its β-κ relationship.A β-κ fitting formula was proposed considering different types of domes.Unlike κ which only represented the rigidity of joints,β represented the stiffness of structures with semi-rigid joints.After calculating the βvalue of 20 bolted-ball joints and 20 welded joints,a classification in terms of the initial stiffness of structure was proposed.According to the proposed classification,the joint was pinned when itsβ value was smaller than 0.3.The joint was rigid when its β value was larger than 0.9.The joint was semi-rigid when its β value was between 0.3 and 0.9.The influence of relative out-plane rigidity of joint,κ1,and relative in-plane rigidity of joint,κ2,on the elastic stability of two types of single-layer spherical domes was investigated in Chapter 7.A criterion was established to detect member buckling of rectangular section members.By the proposed criterion,member buckling could be divided into three types:strong axis buckling,weak axis buckling,strong axis and weak axis buckling.According to the simulation,for those domes with small κ1,the load of load-displacement curve rapidly declined after it hit the peak which was quite similar to the domes with pinned joints.For those domes with relative big κ1 value,the dome remained quite capacity after the curve hit the peak which is similar to the domes with rigid joints.The decrease of κ2 may reduce capacity of domes by weakening the member’s stability about weak axis.But the change of κ2 had no influence on the form of load-displacement curve.