The inverted pendulum pedestrian model (IPM) for walking on laterally-oscillating structures, originally proposed by Macdonald [1], has been recently calibrated using data from pedestrians walking on a laterally-oscillating instrumented treadmill and generalised for predictive use in Czaplewski et al. [2]. The former task was accomplished by defining an empirically-derived foot placement control law. The latter task was accomplished by relating the parameters of this law to the basic anthropometric and gait characteristics of the pedestrian. Closed-form solutions for the long-term average lateral forces obtained from the generalised IPM were then derived in Czaplewski & Bocian [3] based on the framework introduced by McRobie [4]. These solutions were used to obtain the probabilistic lateral dynamic (in)stability criteria for structures subjected to pedestrian loading presented in this paper. A framework introduced in Bocian et al. [5] is used in which stability requirements are expressed in terms of the pedestrian Scruton number and the critical number of pedestrians. To achieve this goal it was necessary to propose a framework for defining a statistical model of the anthropometric parameters used within the IPM solutions, relevant for a given population of pedestrians. It was also necessary to define IPM validity criteria enabling spurious solutions to be omitted from the analysis. To make the proposed structural stability criteria applicable in engineering practice, a framework had to be defined enabling simplified envelopes of the self-excited forces to be obtained. The proposed stability criteria are evaluated based on two case studies of bridges prone to pedestrian-induced lateral dynamic instability. The relatively recent occurrence of instability on the Squibb Park Bridge and its consequences are presented here in detail, as this case is currently little known in the structural engineering community.
