A Study on Design Parameters and Aerodynamic Stability during Construction Stages for a Cable-stayed Suspension Bridge

Abstract

A cable-stayed suspension bridge, which can be applicable to road and railway bridge, is investigated both parameter study on structural characteristic and study on construction sequence to secure aerodynamic stability. The cable-stayed suspension bridge with the main span length of 1408m is considered as an example bridge and this bridge accommodates eight road lane and two railway track. Parametric study is carried out. Two design parameters: suspension-to-span ratio and length of transition part are considered and studied for their effects on the structural behavior under live loads which consist of trains and road vehicles. As a result, a suspension-to-span ratio of 0.22to 0.56 is effective to increase the overall rigidity of structure as compared to responses of cable-stayed bridge and suspension bridge. As the length of suspended portion in main span increases, the vertical displacement of the deck gradually increases and the negative vertical bending moment of deck at the junction between cable-stayed parts and suspended part in main span sharply increases. Also, the cable tension in the longest hanger rapidly increases due to different stiffness in two structure systems namely the cable-stayed part and the suspension part. This can lead to fatigue problems which can be solved by installing the transition part. To investigate the effect of the transition parts, the ratio of transition part to cable-stayed part is changed from 0 to 0.45, by adding additional hangers in the cable-stayed part. As a result, the increase of the transition part is effective to reduce the cable tension in the longest hanger. The transition part to cable-stayed part ratio ranging from 0.1 to 0.32 is favorable for this case study bridge. In the long-span cable-supported bridges, construction stage has lower stiffness relative to completed stage and is vulnerable to vibration by wind. Therefore, aerodynamic stability in construction is a major design issue. Based on the deck erection, two different construction schemes are considered to investigate aerodynamic stability of construction scheme by buffeting analysis for the cable-stayed suspension bridge. The first construction scheme is the construction Plan 0 (series sequence) and the second scheme is the construction Plan 1(simultaneously construction sequence). As a result, applying construction Plan 0 scheme, aerodynamic stability of the suspended deck in construction phase is assured. However, one of the hangers is required to increase the cross-sectional area or adjusts its length after installation in order to secure aerodynamic stability. In case of applying construction Plan 1, the excessive rigid body torsional deformation in the suspended deck is found in the initial construction stage due to the rigid body motion of the suspended deck by the vertical mode of main cable. In order to control the rigid body torsional displacement of deck, X-Type bracing, Rigid beam and Strut system are considered as structural stabilization measures. The most effective structural stabilization measure is the strut system by installing on the main cables. When construction Plan 1 scheme with Strut system, aerodynamic stability is possible and construction period can be reduced by 48 days compared to construction Plan 0 as series construction scheme. However, it is required to have proper construction management of two type of bridge structure according to simultaneous construction in both deck of cable-stayed parts and suspended part. The lifting gantry can be applicable for an aerodynamic stabilization measure to control the rigid body torsional deformation during erection of suspended decks.