| With the development of ground motion observation technology,scholars have realized that ground motion not only contains translational components but also rotational components.Various earthquake damage phenomena and a large number of scholars’ studies have shown that the impact of rotational components of ground motion on engineering structures cannot be ignored.However,most of the seismic design and theoretical research of highway bridges in China focus on the translational components of ground motion,without considering the possible impact of rotational components of ground motion on bridge structures.Simply supported beam bridges are widely used in highways and municipal engineering in China.They are prone to displacement of the main beam and collision under earthquake action,and collision is an important cause of bridge structural damage.At present,most scholars’ research only focuses on bridge structure collisions under the action of seismic translational components,and there is relatively little research on bridge structure collisions under rotational seismic actions.To this end,the following work has been carried out:1.Studied the synthesis theory and method of ground motion rotational components,selected 14 sets of measured data of ground motion translational components,based on elastic wave theory,synthesized the ground motion rotational components using the SSP method,and analyzed their ground motion characteristics.The main conclusions are as follows:(1)In most cases,the peak angular acceleration of the torsion component in the rotation component of the ground motion is greater than the peak angular acceleration of the swing component.(2)Compared to the translational component of ground motion,the rotational component of ground motion contains more high-frequency components,especially those with frequencies above 10 Hz,and the rotational component contains more highfrequency components compared to the torsional component;In addition,the angular acceleration response spectrum of the rotational component of the ground motion has a large amplitude in the period of 0.1s.Therefore,for engineering structures with smaller structural periods,attention should be paid to the potential threat of the rotational component of seismic motion to their dynamic response.2.To study the impact of rotational components of seismic motion on the collision effect of bridge structures,a refined finite element model of a simply supported beam bridge was established based on the SAP2000 finite element platform.The collision effect of a simply supported beam bridge was analyzed under the conditions of translational component,translational component plus torsional component,translational component plus sway component,and six components of seismic motion.The main conclusions are as follows:(1)The rotational component of seismic motion has a significant impact on the collision response of simply supported beam bridges.The rotational component not only increases the peak collision force between the contact unit and the stop,but also changes the rotation pattern of the main beam,thereby affecting the collision pattern between the main beam and the contact unit and the stop.Excessive collision force can cause damage to the bridge structure,and attention should be paid to the influence of the rotational component of seismic motion on the collision response of simply supported beam bridges.(2)The impact effect has a significant impact on the response of simply supported beam bridges.After considering the impact effect,the longitudinal bending moment at the pier bottom of most bridge piers decreases,while other internal forces at the pier bottom increase.After considering the collision effect,the rotational component of seismic motion has a significant impact on the displacement of the support and the internal force response at the pier bottom.The maximum increases in the rotational component on the longitudinal displacement of the support,the transverse bending moment at the pier bottom,and the torque response at the pier bottom are 9.6%,10.6%,and 37.6%,respectively.In the seismic design of simply supported beam bridges,attention should be paid to the influence of the rotational component of seismic motion on the displacement of the support and the internal force at the pier bottom.(3)The influence of different components in the rotational component of seismic motion on the response of bridge structures is different.The sway component in the rotational component has a significant impact on the lateral bending moment and support displacement response at the pier bottom,while the torsion component has a significant impact on the longitudinal shear force and torque response at the pier bottom.3.To study the impact of different parameters on the collision effect of simply supported beam bridges under rotational seismic motion,the initial clearance,collision stiffness,and seismic apparent wave velocity of the contact element were selected.The impact of bridge structural parameters and seismic motion parameters on the collision effect of simply supported beam bridges was analyzed under the conditions of translational component,translational component plus torsional component,translational component plus sway component,and six component seismic motion.The main conclusions are as follows:(1)Under rotation ground motion,the peak collision force and collision frequency of contact elements decrease with the increase of initial clearance.The rotation component has a greater impact on the longitudinal bending moment response of the pier bottom when the initial clearance is small.Considering the rotation component,the maximum increase is 5.5% when the initial clearance is 4cm;When the initial clearance is large,the rotational component has a greater impact on the longitudinal shear force at the pier bottom and the longitudinal displacement response of the support.After considering the rotational component,the maximum increase at the initial clearance of8 cm is 11.0% and 46.6%,respectively.Both small and large initial clearances under rotational seismic motion have adverse effects on the response of bridge structures,and various factors should be considered for reasonable values in engineering.(2)Under rotation ground motion,the peak collision force of the contact element increases with the increase of collision stiffness,while the number of collisions decreases.When the collision stiffness is small,the rotational component has a greater impact on the longitudinal displacement response of the support at the middle pier.When the collision stiffness is large,the rotational component has a greater impact on the longitudinal displacement response of the support at the abutment.When the collision stiffness is 1.0k,the rotational component has the greatest increase in torque at the pier bottom,which is 37.6%;When the collision stiffness is 1.5k,the rotational component has the greatest increase in the transverse bending moment at the pier bottom,which is11.0%.The influence of rotational components on the response of bridge structures varies with the change of collision stiffness.When the collision stiffness increases to a certain extent,the influence of rotational components on each response tends to be gentle.(3)Under rotation ground motion,there is a situation where the peak collision force and collision frequency of the contact element are greater than the uniform excitation after considering the traveling wave effect.After considering the traveling wave effect,the influence of the rotational component of seismic motion on the longitudinal displacement of the support and the internal force response of the pier bottom is more significant.When the apparent wave speed is 300m/s,the rotational component has the largest increase in the longitudinal displacement of the support,at 27.6%;At a visual wave speed of 500m/s,the rotational component has the greatest increase in the longitudinal bending moment,longitudinal shear force,and torque at the pier bottom,which are 8.6%,14.8%,and 52.9%,respectively. |
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