Arun Menon

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: I. Parametric Study

Response of masonry walls to out-of-plane excitation is a complex, yet inadequately addressed theme in seismic analysis. The seismic input expected on an out-of-plane wall (or a generic “secondary system”) in a masonry building is the ground excitation filtered by the in-plane response of the walls and the floor diaphragm response. More generally, the dynamic response of the primary structure, which can be nonlinear, contributes to the filtering phenomenon. The current article delves into the details and results of several nonlinear dynamic time-history analyses executed within a parametric framework. The study addresses masonry structures with rigid diaphragm response to lateral loads. The scope of the parametric study is to demonstrate the influence of inelastic structural response on the seismic response of secondary systems and eventually develop an expression to estimate the seismic input on secondary systems that explicitly accounts for the level of inelasticity in the primary structure in terms of the displacement ductility demand. The proposed formulation is discussed in the companion article.

SEISMIC HAZARD ASSESSMENT OF THE HISTORICAL SITE OF JAM IN AFGHANISTAN AND STABILITY ANALYSIS OF THE MINARET

The Minaret of Jam in Afghanistan was recently included in UNESCOs List of Worlds Endangered Monuments. The minaret is the worlds second tallest (∼60 m) after the Qutub Minar in New Delhi and it is also one of the oldest (∼800 years). It is situated at the centre of the Hindukush range in the Ghor Province at the junction of Rivers Hari-Rud and Jam-Rud, at an elevation of 1900 m. The Minaret of Jam is in danger of collapse due to a 3.4° northward inclination inducing high stresses in its deteriorated brick masonry. The precarious conditions of the monument render it highly vulnerable to earthquakes. Therefore prior to any intervention to protect it, an assessment of the seismic hazard at the site, followed by an evaluation of the towers seismic vulnerability, is of foremost importance. This article illustrates the results of the seismic hazard assessment of the archaeological site of Jam using both the probabilistic explanation (PSHA) and the deterministic explanation (DSHA) approaches. Uncertainty in PSHA has been handled within a logic-tree framework. Uniform hazard response spectra have been computed for return periods of 72, 224, 475 and 975 years. The earthquake input defined by the seismic hazard assessment of Jam has then been used to perform the dynamic analysis of the minaret. The latter has been carried out using a lumped mass approach and a 3D finite element model, accounting in both cases for dynamic soil-structure interaction.

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: II. Formulation

The seismic input expected on an out-of-plane wall (or a generic secondary element) in a URM building is the ground excitation filtered by the in-plane response of the walls and the response of the floor diaphragms. More generally, the dynamic response of the primary structure, which can be nonlinear, contributes to the filtering phenomenon. Inelastic response of the primary structure can alter the secondary system response considerably in comparison to that under elastic structural response. The current article proposes a semi-analytical formulation to estimate the acceleration demand on an out-of-plane URM wall that explicitly takes into account the level of inelasticity in the primary structure in terms of the displacement ductility demand. A simplified approach to determine the acceleration profile over the height of a structure is also introduced. The formulation is based on statistical evaluation of the results of several inelastic time-history analyses treated within a parametric framework, which are presented in the companion article.

Graph-Based Clustering for Apictorial Jigsaw Puzzles of Hand Shredded Content-less Pages

Reassembling hand shredded content-less pages is a challenging task, with applications in forensics and fun games. This paper proposes an efficient iterative framework to solve apictorial jigsaw puzzles of hand shredded content-less pages, using only the shape information. The proposed framework consists of four phases. In the first phase, normalized shape features are extracted from fragment contours. Then, for all possible matches between pairs of fragments transformation parameters for alignment of fragments and three goodness scores are estimated. In the third phase, incorrect matches are eliminated based on the score values. The alignments are refined by pruning the set of pairwise matched fragments. Finally, a modified graph-based framework for agglomerative clustering is used to globally reassemble the page(s). Experimental evaluation of our proposed framework on an annotated dataset of shredded documents shows the efficiency in the reconstruction of multiple content-less pages from arbitrarily torn fragments.

Biaxial Effects in Unreinforced Masonry (URM) Load-Bearing Walls

Under seismic loading, a structure may be subject to simultaneous in-plane and out-of-plane actions. Existing simplified methods like the storey-shear mechanism to determine the shear capacity of masonry structures neglect the out-of-plane effects leading to a non-conservative seismic assessment. In this paper, an analytical model is developed to evaluate the in-plane shear capacities of unreinforced masonry (URM) walls, in the presence of additional out-of-plane displacement. Results from this paper demonstrate that the additional out of displacements alter both the in-plane shear capacity and failure mechanism of the wall. The sensitivity of the interaction to the axial load on the wall is also studied. The proposed model is validated with non-linear finite element analysis. The developed model can be used to determine the reduced shear capacity of URM walls if the mid-height out-of-plane displacement is known. The biaxial interaction of URM walls is also studied dynamically. The model is extended to the framework of the storey-shear mechanism to study the effect of out-of-plane displacements at the global level.

Structural Behaviour of Dry Stack Stone Corbelled Vaults Under Lateral Support Movement

The preservation or restoration of any structural typology requires understanding of the load transfer mechanism under the influence of external actions. Scarce literature on the structural behaviour of existing dry stack stone corbelled arches and vaults has motivated the present study. The objective of the study is to have a better understanding on the failure mechanisms of corbelled vaults under different types of support movement, e.g. translations and rotations, both lateral (inward and outward) and vertical and the in-plane and out-of-plane directions. The current paper examines the in-plane behaviour under relative outward lateral spreading of the support. A test setup is specially fabricated for evaluating these lateral support movements in dry stone corbelled vaults. The prototype of the test model chosen for study is one of the existing entrance vaults of Ta Prohm Temple, Cambodia restricting to the bare arch form, a 2D representation. The angle of repose of a typical vault varies between 45 to 60°. The arch considered here is of 56° of angle of repose. Digital photogrammetric technique has been utilized in the study to capture the deformed geometry, which has proved to be very useful in monitoring the displacements of the rigid blocks. From the study it is concluded that these corbelled arch systems under relative in-plane outward support movement tend to fail by overturning inwards because of the rocking failure being dominant over sliding by virtue of the structural configuration, and available sliding friction.

Structural Behaviour of Gopurams in South Indian Temples

The multi-storied masonry “Gopuram” or the ceremonial entrance gateway, an ubiquitous structure in a South Indian temple, was a feature introduced circa 14th c. AD in order to confer architectural status to structurally insignificant ancient shrines. The gopurams of the Meenakshi Temple in Madurai (1600 AD), the Ranganathaswamy Temple in Srirangam (17th c. AD) and the Ekambareswar Temple in Kancheepuram (16th c. AD), 52 m, 72 m and 59 m tall, respectively, are representative of the highly evolved Dravidian temple architecture. The current research is an attempt to understand the structural behaviour of the gopuram with a focus on a centuries-old incomplete structure in the town of Thiruvellarai in Tamil Nadu. The paper presents outcomes of detailed field and laboratory investigations on the sub-structure, the superstructure and structural materials of the gopuram, that provide insight into the structural configuration of the gopuram. It then examines the structural response to gravity and lateral forces, through non-linear finite element models of the structure. One of the significant aspects studied is the role of the core masonry in the structural response of the multi-leaf masonry structure of the gopuram. In addition the role of floor diaphragms in the structural stability of the gopuram is investigated. The outcome of the study is expected to provide important insights to the reasons for structural distress and collapse of such structures, particularly the Vijayagopuram at Srikalahasti in Andhra Pradesh in South India that collapsed in May 2010.

An Exploratory Study on Project Delivery Frameworks for Heritage Conservation in India

The degree of sophistication required for governing a project depends on its complexity and scale. Although most heritage conservation projects have smaller budgets than new construction, the high uncertainty and complexities, necessitate robust project management framework. A well-defined project delivery framework is a key success factor for heritage conservation projects. India, with its rich cultural and geographical diversities, and more than 5000 years old civilization, has innumerable heritage sites spread across the country. Heritage conservation is a highly fragmented sector in India, with different agencies responsible for the protection and conservation of various heritage structures, and the modes, methods, and extent of conservation witnessed at these sites are of divergent nature. The objective of this paper is to study the different types of project delivery models used for heritage conservation in India. The authors have done an exploratory study on 50 heritage sites, where restoration projects are currently being executed or have been recently completed. The available project documents have been reviewed, and conservation professionals and other main stakeholders have been interviewed to map the project governance frameworks used for the projects. The 50 projects studied were categorized based on factors such as heritage category, ownership, implementing agency, scale of project, project frequency, funding pattern, apart from project delivery model and the relation between the factors studied analytically. The results indicate that Project Frequency and Funding Pattern are the significant factors influencing the selection of project delivery models for heritage conservation.

Restoration of Reinforced Lime Concrete Sunshades of a Century Old Heritage Building in New Delhi, India

The Rashtrapati Bhavan, the official residence of the President of India, is a Grade-I heritage structure. The reinforced concrete cantilever sunshades in this building are at a height of about 20 m above ground and span about two-kilometer along the perimeter of the building. In the late 1990s, some sunshades experienced corrosion and were repaired using polymer modified cementitious mortar. However, these repaired sunshades and others are now exhibiting severe corrosion and concrete spalling- posing a serious falling hazard for visitors and inhabitants. This paper presents a systematic evaluation of the concrete used in the sunshades and the assessment of corrosion and structural conditions of the sunshades. Concrete was found to be made of non-hydraulic lime and carbonated - indicating high probability of corrosion. Hence, about 200 sunshade locations from various parts of the building were visually and non-destructively assessed and distress-maps were developed. For this, an instrumented hammer was used on 15 test points per sunshade panel area (of about 1 × 2 m size). Based on the impulse waveform patterns, estimated strengths and visible damage, the panels were classified into distress levels of negligible, moderate and severe. About 58 to 86% of the sunshades were found to be severely damaged. Also, service level load test was conducted (upto a load of 75 kN) at a representative location, to assess the effect of corrosion on the load-deflection behaviour of the cantilever. The possible repair strategy and challenges associated with adopting conventional methods, are discussed in the paper.

Analysis of the Dome of India’s Presidential Residence

The Rashtrapati Bhavan or the Presidential Residence on Raisina Hill in New Delhi is an iconic structure designed by Sir Edwin Lutyens in the Indo-Saracenic style and completed in 1929. The structure is made of brick masonry, sandstone cladding, lime and reinforced cement concrete. This paper gives an insight into the investigative process that was followed to determine the causative mechanism of the observed structural distress in the inner dome of the central double-dome of the Rashtrapati Bhavan. During the visual scrutiny of the building, a crack of significant dimension in the north-eastern niche of the domed hall and a small crack in the diametrically opposite niche were detected. In order to evaluate the severity of the observed cracks, a systematic and holistic approach that comprised of historical and geometric surveys, assessment of the sub-structure morphology and the use of relevant non-destructive and minor destructive tests on the superstructure was adopted. The findings from the above-mentioned sources, served as valuable input for the finite element model of the structure, that was developed using DIANA. The non-linear gravity and pushover analyses conducted on the model confirmed the speculation made on the basis of the visual and geometrical assessment, that the opening of the stairwell in the vicinity of the affected niche presents an inherent weakness at the drum of the dome. The paper describes the in-situ tests, relevant structural features for the numerical analysis, modelling aspects and the results from the analysis.