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Heritage masonry structures require detailed monitoring during nearby underground construction, to address the concerns of building owners and mitigate uncertainties relating to the soil–structure system. This paper discusses innovative displacement and strain monitoring of a listed masonry church undergoing ground movements due to nearby tunnelling in London Clay. In addition to conventional surveying and tilt monitoring, laser scan displacement monitoring and fibre optic strain sensing was conducted. Prior to construction, point clouds of the structure were used to map pre-existing geometric distortions in the structure. During construction, detailed monitoring of displacements and strains was conducted across the building facades and the tower. The same techniques were also used to monitor the painted dome of the church where conventional displacement monitoring was not feasible. With a focus on the new engineering insight provided by the innovative monitoring techniques, the impact of the underground construction activities on the church is discussed in this paper. The proposed sensing techniques provide new data on the influence of pre-existing damage and tunnel advance on soil–structure interaction.

Motivated by the rocking motion of non-rigid structures during earthquakes, this paper investigates the rocking behaviour of laterally flexible oscillators. Previous studies in this area utilised ad hoc assumptions to consider transitions between different motion phases at impact. Some models explored direct transitions between two rocking phases assuming that elastic translational velocities remain the same, while others assumed the dissipation of all vertical momentum after a rocking phase, leading to a full contact phase upon impact. In this paper, an improved impact model is proposed, where consistent mechanical principles are used to determine the phase transition criteria. The model departs from the principle that the spring and damper elements of the oscillator cannot transfer horizontal impulses over infinitesimally small durations. Alongside other mechanical constraints, this principle yields a series of momentum equations, which are solved to determine the post-impact velocities when transiting from one rocking phase to another. Through these equations, it is shown that a transition to full contact implies a specific locus of the vertical impulse from the support medium. Analytical and numerical investigations are then conducted to comparatively evaluate the new impact model. It is demonstrated that the new impact model yields equivalent results to established rigid rocking impact models for effectively rigid structures and resolves long-standing issues associated with excessive energy dissipation observed in previous models. Time histories of free rocking motion and stability analyses under pulse excitations are used to illustrate and generalise the findings for a range of geometries.

Controlling building displacements induced by tunnelling is a major issue in densely urbanised areas, particularly for listed heritage structures. Major tunnelling projects provide opportunities to assess the ability of advanced numerical models to address this issue, in conjunction with the large amount of monitoring data that are gathered during the works. This paper considers the case of two Grade-I listed buildings (St. Mary Abchurch and Mansion House) affected by the Bank Station Capacity Upgrade in London (UK) where complex excavation works were conducted to improve the existing underground infrastructure. Both conventional and innovative monitoring was carried out to control the effect of tunnel construction on these buildings. Following the works, three-dimensional finite element analyses were conducted by adopting a semi-coupled modelling approach. In these analyses, the pre-existing damage in the buildings prior to tunnelling has been considered by adjusting the properties of embedded solids that are used to idealise the structure. The analyses also considered salient aspects that are often neglected in routine risk-assessment procedures, such as the excavation modelling sequence covering both pilot tunnelling and enlargement, the skew building-tunnel alignment, and the effect of closely spaced tunnel excavations on surface ground deformations. The results highlight the challenges associated with idealising historic structures with semi-coupled models; nevertheless, they encourage the integrated use of innovative monitoring systems and advanced numerical modelling as a tool to control the process of tunnel excavation in complex urban environments.

This paper proposes simple numerical models that simulate the influence of tunneling-induced ground movements on masonry buildings founded on shallow strip footings. The focus is on develop...

© 2018 New Zealand Society for Earthquake Engineering. All rights reserved. Rocking action at the foundation-structure interface has long been proposed to isolate structures from strong ground motion. In this paper, the fundamental concept of rocking isolation is examined in depth to guide further design efforts. This is achieved by first deriving an analytical model of a flexible structure freely rocking on rigid ground. Decomposing the coupled equations of motion of the model into their modal components provides new information on the mechanics of rocking isolation. After identifying the salient parameters needed to quantify rocking isolation, equations to predict the lateral accelerations, base shear and overturning moments arising during rocking are provided. The analytical model and the simplified equations are then validated using some of the earliest experiments on rocking structures, which were completed in New Zealand. These validations clarify poorly understood phenomena concerning rocking isolation, such as how rocking and vibrations of the structure couple, how this influences the excitation mechanisms of the structure, resulting in seismic shear forces and overturning moments larger than those required for uplift. The findings provide an analytical basis for designing efficient rocking systems that successfully limit force demands.

Summary This paper presents a new analytical model for describing the large rocking response of an elastic multi-mass structure resting on ideally rigid ground. Using the experimental results from a rocking steel column, the ability of the proposed analytical model to estimate the rocking and translational acceleration response under free vibration, pulse and earthquake excitations is evaluated. It is observed that the classical treatment of impact may result in an unrealistically large transfer of energy to vibrations. Therefore a new Dirac-delta type impact model that spreads the effects of impact over time and space is proposed. The use of a Dirac-delta model and accurate restitution factors play a pivotal role in prediction of rocking and acceleration responses. In order to characterize the nonlinear response better, a modal analysis of the linearized system is proposed. With this approach, the vibration mode frequencies and shapes during rocking action were determined. A comparison of analytical and experimental modal estimations suggests good agreement. The results emphasize that the vibration characteristics of several vibration modes are affected by rocking action, and these modes may be excited at impact. Copyright © 2016 John Wiley & Sons, Ltd.

This article presents the results of free vibration and earthquake excitation tests to investigate the dynamic behavior of freely rocking flexible structures with different geometric and vibration characteristics. The primary objective of these tests was to identify the complex interaction of elasticity and rocking and discuss its salient effects on the rocking and vibration mode frequencies, shapes and excitation mechanisms. The variability of response is discussed, including critical investigation of the repeatability of the tests. It was found that the variability in energy dissipation and energy transfer to vibrations at impact may lead to significantly different responses to almost identical excitations.

Predicting the displacement and force response of flexible rocking structures to ground motion is important for their assessment and design. Insofar as practical, it is desirable to use simple mechanical models to make these predictions. However, the complex coupling between rocking and vibration makes accurate predictions with simple models difficult. In this paper, the use of semi-coupled equivalent models to approximate the dynamic response of multi-mass structures rocking on rigid ground is evaluated. These equivalent models feature a two-degree of freedom coupled rocking oscillator to describe the interaction of rocking and the first mode of vibration, and uncoupled linear elastic oscillators to describe higher mode vibration response. To evaluate these equivalent models, the modal components of the dynamic response of multi-mass structures are first determined. These components highlight the critical influence of the excitation of vibration modes at impact. Then, further investigations are carried out by comparing equivalent model simulations to recent shake table tests and multi-mass analytical model simulations. These comparisons reveal that the equivalent models can capture the rocking response accurately for a realistic range of displacements, if a new ground acceleration scaling term is adopted. However, the uncoupled linear elastic oscillators do not consider excitation at impact and consequently, the equivalent models do not capture the acceleration response adequately. Therefore, on the basis of the analytically identified modal components, a further modification that improves the equivalent model acceleration predictions is proposed and validated.

The rocking response of structures subjected to strong ground motions is a problem of ‘several scales’. While small structures are sensitive to acceleration pulses acting successively, large structures are more significantly affected by coherent low frequency components of ground motion. As a result, the rocking response of large structures is more stable and orderly, allowing effective isolation from the ground without imminent danger of overturning. This paper aims to characterize and predict the maximum rocking response of large and flexible structures to earthquakes using an idealized structural model. To achieve this, the maximum rocking demand caused by different earthquake records was evaluated using several ground motion intensity measures. Pulse-type records which typically have high peak ground velocity and lower frequency content caused large rocking amplitudes, whereas non-pulse type records caused random rocking motion confined to small rocking amplitudes. Coherent velocity pulses were therefore identified as the primary cause of significant rocking motion. Using a suite of pulse-type ground motions, it was observed that idealized wavelets fitted to velocity pulses can adequately describe the rocking response of large structures. Further, a parametric analysis demonstrates that pulse shape parameters affect the maximum rocking response significantly. Based on these two findings, a probabilistic analysis method is proposed for estimating the maximum rocking demand to pulse-type earthquakes. The dimensionless demand maps, produced using these methods, have predictive power in the near-field provided that pulse period and amplitude can be estimated a priori. Use of this method within a probabilistic seismic demand analysis framework is briefly discussed.

Numerous structures uplift under the influence of strong ground motion. Although many researchers have investigated the effects of base uplift on very stiff (ideally rigid) structures, the rocking response of flexible structures has received less attention. Related practical analysis methods treat these structures with simplified 'equivalent' oscillators without directly addressing the interaction between elasticity and rocking. This paper addresses the fundamental dynamics of flexible rocking structures. The nonlinear equations of motion, derived using a Lagrangian formulation for large rotations, are presented for an idealized structural model. Particular attention is devoted to the transition between successive phases; a physically consistent classical impact framework is utilized alongside an energy approach. The fundamental dynamic properties of the flexible rocking system are compared with those of similar linear elastic oscillators and rigid rocking structures, revealing the distinct characteristics of flexible rocking structures. In particular, parametric analysis is performed to quantify the effect of elasticity on uplift, overturning instability, and harmonic response, from which an uplifted resonance emerges. The contribution of stability and strength to the collapse of flexible rocking structures is discussed. © 2012 John Wiley & Sons, Ltd.