Aerodynamic Admittance for Buffeting Analysis of a Twin-Box Deck with Barriers: A Combined Experimental–Numerical and Field Validation Study

Aerodynamic admittance functions (AAFs) are a key parameter determining the accuracy of buffeting analysis in long-span bridges. However, the presence of barriers and central gap complicates the aerodynamic response of in-service twin-box decks, thereby increasing uncertainties in AAF identifications when relying solely on traditional wind tunnel tests (WTTs). To improve the identification accuracy and reliability, the AAFs of a twin-box deck with barriers are investigated here by combining active wind tunnel tests, large eddy simulations (LESs), and field validations. Firstly, the AAFs in narrow-banded sinusoidal gusts are identified by combining the WTTs using the active gust generator and LESs. Then, the strongest wind event at the bridge site recorded over the service life of the bridge is simulated using LESs using a synthetic inflow to identify the AAFs under the action of broad-banded turbulent wind. The effects of barriers on AAFs are isolated by comparing the results obtained on the bare deck with those on the in-service geometry. Finally, time-domain buffeting analysis using four 1-h strong wind events is performed to validate the identified AAFs. Results show that the AAFs identified from active WTTs match well with LESs under both sinusoidal gusts and turbulent inflows, with values notably exceeding the Sears function and quasi-steady value of 1. The increase in AAFs caused by barriers is primarily attributed to reduced lift coefficient derivatives. Buffeting analysis using identified AAFs shows good agreement with field measurements, providing practical guidance for AAF identifications and buffeting estimations of in-service long-span bridges.