Multi-dimensional Seismic Vulnerability Study Of Girder-arch Spandrel Construction On Long-span Deck-arch Bridge

Deck-arch bridges are one of the most commonly used bridge types in mountainous areas due to their aesthetic appearance,lightweight,and spanning capacity.With the improvement and innovation of design and construction techniques,deck-arch bridges are developing towards large spans and diversified structural forms.For smaller spans,the seismic damage of spandrel construction is not very prominent,with most of the damage occurring at the arch ring.However,as the span increases,the height differentiation of the spandrel columns become more significant,resulting in an increased disparity in seismic forces on each column.Consequently,the seismic damage to the spandrel construction becomes more apparent.Therefore,seismic damage of the spandrel construction may become a major conflict in the seismic design of long-span deck-arch bridges.Currently,the seismic research of deck-arch bridges focus on the performance of the arch ring,with little consideration given to the role of the spandrel construction in the bridge failure process,which inevitably leads to inaccuracies in the assessment of the failure probability of the system.In view of this,this thesis conducts a multi-dimensional seismic vulnerability study on the spandrel construction of a long-span deck-arch bridge,and explores the effect of the arch ring on the vulnerability of the spandrel construction by comparing it with a girder bridge with the same structural form.On this basis,it is hoped to apply the existing seismic design methods of irregular girder bridges to the seismic optimization design of spandrel construction.The main contents and conclusions of this article are as follows:(1)Taking a long-span deck-type reinforced concrete arch bridge as the research object,finite element models of the arch bridge,main arch ring,and girder bridge were established using the SAP2000 analysis platform,and their dynamic characteristics were analyzed.Subsequently,the spectral characteristics of the filtered time history at the base of the spandrel columns and the seismic response of critical components under longitudinal,transverse,and vertical loading are investigated.Through a comparative analysis,the influence of the arch ring on the seismic response of the spandrel construction has been revealed.Studies show that the presence of the arch ring enhances the structural flexibility and increases the natural period.The acceleration response spectrum of the filtered time exhibits amplification within the natural period of the structure,with a more pronounced effect for shorter columns.The power spectrum of the filtered time increases in certain low-frequency ranges but significantly attenuates in the high-frequency range.In the horizontal loading direction,the seismic response distribution of the spandrel construction and the girder bridge with the same structural form is the similarity.However,the force response of the spandrel construction components is smaller than that of the corresponding girder bridge components.Moreover,the spandrel construction components generate undeniable force in the longitudinal direction during lateral loading,resulting in noticeable bidirectional load on the components.Generally,the spandrel construction is more sensitive to vertical earthquakes,resulting in larger seismic response compared to the girder bridge with the same structural form.In the overall assessment,the main arch ring has the largest to smallest effect on the seismic response of the spandrel construction under various loading directions,with the order being vertical,lateral,and longitudinal.(2)Determined suitable damage indexs,the seismic weak link of bridges under three-dimensional earthquake were identified by combining the Increment Dynamic Analysis method(IDA)and the Capacity-demand Ratio method(C/D).Then,the fragility curves of components and systems are established through the Three Dimensional Seismic Fragility Analysis method(TDSFA)and the Product of Conditional Marginal method(PCM).On this basis,the influence of vertical earthquake and the seismic input direction for the damage probability is discussed using the vulnerability index.Finally,a comparative analysis has been carried out to clarify the seismic vulnerability of spandrel construction and the influence of the arch ring on the damage probability of spandrel construction.Research has shown that the damage severity of long-span deck-arch bridges follows the order: spandrel column deformation damage,column bending damage,main arch ring bending damage,and column shear damage.The components of the spandrel construction have similar fragility curves to those of the girder bridge,with the high pier columns and bearings being the most severely damaged.The arch ring leads to a greater vulnerability probability of the high column,low column and bearing near the1/4 point to the corresponding girder bridge component,but the spandrel construction components are less likely to be damaged than those on the girder bridge in the remaining cases.Overall,the systemic vulnerability probability of the spandrel construction is less than that of the girder bridge with the same structure form,the presence of the main arch ring is beneficial to the seismic resistance of the spandrel construction.It is essential to consider the effects of vertical earthquakes and the direction of seismic input when designing spandrel construction for seismic resistance.(3)Referring to the seismic design method of irregular girder bridges,this article optimizes the design of spandrel construction by adjusting the stiffness of the bearings and modifying the splitting form,and make relevant recommendations.Research shows that the constraint effect of the superstructure needs to be considered when optimizing the bearing stiffness,and adjusting the bearing stiffness is more to weaken the seismic response of the short column.The continuous system is more conducive to the synergistic seismic resistance of the piers than the simply-supported system,and the best seismic damping effect is achieved in spandrel construction with the uniform short connection.Setting up one of the side spans as a rigid system will facilitate the seismic resistance of the high columns,but the number of spans should not be excessive.After comprehensive optimization the seismic response and vulnerability probability of vulnerable component meet the expected effect.However,the displacement of individual bearings may increase,limit measures need to be installed if necessary.