Issue 3: Sep-Dec. 2015

Alexander Blekherman

Abstract:The paper focuses on the excessive lateral sway motion in footbridges, induced by walking pedestrians, which can be treated as instability of a structure. For its explanation, a nonlinear problem of the dynamical behavior of an elastic pendulum is analyzed. It is shown that simultaneously applied two external vertical and lateral forces (the latter is based on a forced model whose amplitude is a function of a deck vibration) can lead to instability of a footbridge in the case of internal resonance, when the ratio between natural frequencies of vertical and lateral beam modes is about 2:1, and the natural vertical frequency is close to the vertical walking frequency. In this case an increasing control (load) parameter (a static displacement caused by pedestrians) passes through its critical value, the fast growth of the lateral mode is observed, and the vertical mode is saturated. The relation between the proposed model and a corresponding real structure is displayed on an example of a suspension footbridge. The nonlinear differential equations are deduced for describing nonlinear autoparametric coupling vibration of suspension footbridges. It is shown that the averaging nonlinear differential equations of suspension footbridges and an elastic pendulum are similar, what allows considering the latter as their model. In the case of lack coupling between modes, the same mathematical model describes parametric resonance for the lateral mode. The theoretical results of the analysis of the model and experimental measurements performed for the London Millennium Bridge, the Changi Mezzanine Bridge (Singapore) and the Solferino Bridge (Paris) are compared and discussed. Based on the above-mentioned test results, it is discussed the reason for arising a single frequency lateral response after losing stability of the system in the case of external vertical random excitation. It is shown that the model describes correctly the qualitative features of dynamical behavior of footbridges in the case of a wideband (or narrowband) random modal excitation.

International Journal of Bridge Engineering, Vol. 3, No. 3, 2015: pp. 1-33

Nicos Makris, Haris Alexakis

Abstract:More than a century ago Milankovitch presented for the first time the correct and complete solution for the theoretical minimum thickness, t, of a semicircular masonry arch with radius, R (t/R=0.1075). This paper uses a variational formulation approach and shows that this solution is not unique and that it depends on the stereotomy exercised.

International Journal of Bridge Engineering, Vol. 3, No. 3, 2015: pp. 35-42

Panayiotis Papanikolas, Aris Stathopoulos-Vlamis, Akis Panagis, Olivier Flamand

Abstract:Structural monitoring systems produce an enormous volume of data, the storage and processing of which is both costly and difficult. To tackle this problem a different approach can be applied using sparse data. The exploration of such data assisted in acquiring all vortex shedding deck excitation events, in order to rebuild vibration history and evaluate fatigue risk.

International Journal of Bridge Engineering, Vol. 3, No. 3, 2015: pp. 43-52

Jørgen S. Steenfelt, Brian Foged, Anders H. Augustesen

Abstract:The Izmit Bay Suspension Bridge, app. 50 km east of Istanbul, crosses the Sea of Samara with a main span of 1550 m. The foundation of the bridge poses interesting challenges in that the bridge site is in a highly seismic region. Moreover the ground profile ranges from Dolomitic Limestone to a thick sandwich of silty sand and clay layers overlying the bedrock.

International Journal of Bridge Engineering, Vol. 3, No. 3, 2015: pp. 53-68