Arun Menon

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 contentless pages from arbitrarily torn fragments.

Normative frameworks for seismic retrofit of existing unreinforced masonry buildings across the world involve an initial phase of assessment procedures based on engineering principles and quantitative methods. This is followed by guidelines for the retrofit of such structures and methods for the safe implementation of the retrofit techniques. These guidelines are regulatory in nature but based on the conclusions derived from the evaluation process. In the Indian context, there exist comprehensive databases covering the typologies of unreinforced masonry (URM) buildings and strengthening guidelines. However, a normative framework with a quantitative basis for the assessment of existing URM buildings is absent. Since the strengthening guidelines are merely prescriptive in nature, the analytical basis for choosing a particular strengthening scheme becomes uncertain and is left to the discretion of the engineer. This paper identifies and addresses the gaps in the Indian standards, developing a quantitative basis for assessment of existing URM buildings. A possible seismic assessment framework has been proposed by addressing the critical concerns and challenges and elucidated through a demonstrative example.

Buildings characterized by torsional irregularity are notorious for their vulnerability to earthquakes. However, most fragility/vulnerability models used for regional seismic risk assessment fail to distinguish between buildings with torsionally balanced and unbalanced configurations. The present study aims to develop a seismic fragility model sensitive to torsional irregularity for low-rise non-ductile RC moment frame buildings. To this end, a numerical investigation centred on 13 three-storied plan-asymmetric models, each characterized by a distinct combination of normalized stiffness eccentricity, torsional radius to mass radius of gyration ratio and normalized strength eccentricity, is presented. Using high-dimensional model representation (HDMR), a metamodel for the maximum inter-storey drift under bi-directional seismic action is calibrated, considering average spectral acceleration and the above trio of torsional irregularity descriptors (TIDs) as the predictor variables. Carrying out numerical simulations on limit state functions formulated using the above demand model and appropriate capacity thresholds, the seismic fragility is estimated. The parameters of a lognormal fragility function compatible with the above estimates are determined using the method of maximum likelihood. A strong correlation is observed between the TIDs and the fragility function parameters. This reinforces the importance of accounting for all three TIDs while rating the seismic fragility of a building. Using least-square error minimization technique, a functional relationship is established between the fragility model parameters and the TIDs. The framework described herein provides a simple, yet rational means to develop the next generation of seismic fragility models accounting for one of the most critical factors governing seismic behaviour––‘torsional irregularity’.

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.

Dry stack stone masonry constructions, such as corbelled vaults, pillared halls composed of monolithic components, and structural walls generally undergo rigid body failure mechanisms such as overturning or sliding under lateral action caused by support settlements or earthquake shaking. Such structural systems rely purely on self-weight and sliding resistance through friction to resist lateral actions. To develop any reliable numerical model for the damage assessment of these stone masonry structures, knowledge of joint normal and shear stiffness along with friction parameters is essential. The objective of the present work is to estimate these joint parameters for dry masonry joints through experimental tests. Joint shear test and axial compression test have been performed on granite stone blocks. Role of various aspects such as surface roughness, pre-compression levels, moisture condition (dry and wet) and dilatancy on the joint behaviour are considered in the 54 joint shear tests conducted. Numerical simulation of the joint behaviour using a model based on discrete element method (DEM) with parameters obtained from the experiments demonstrates a direct application of the outcome of the experiments.

The historical fort of Bhatner at Hanumangarh, Rajasthan in India was built around 1700years ago using burnt clay bricks with lime mortar. This fort complex has three gateway adorned with arches and tri-arch colonnaded spaces.These gateway structures are significantly distressed and several cracks on arches and vaults of gateway possibly are observed. The current paper presents a detailed geotechnical and structural investigation to find out the root cause of the distress in the fort. For geotechnical Investigation, the methodology followed for the geotechnical test comprises of appropriate sub- soil exploration including field investigation at 4 bore hole locations and relevant laboratory tests on soil samples for determining allowable bearing pressure of the soil. In structural investigation, settlement analysis has been performed on the 3D Finite element model of the fort considering gravity load and earth pressure on the fort wall using TNO DIANA software package. The study concludes that the distresses shown on the structure especially at Gateway 2 and 3 are due to soil settlement.

Macro-element approach for modelling and seismic analysis of existing masonry structures, where structural system is discretized into deformable horizontal and vertical equivalent frames and rigid nodes, is preferred over micro-modelling approaches due to the complexities of material non-linear characterization and computational effort. Most macro-element modelling approaches make vital assumptions on out-of-plane mechanisms, a recurrent failure mode in existing masonry structures. Idealisations in the modelling of diaphragm action of the horizontal structural system are also rather empirical. In fact, non-linear static analysis (pushover)- based assessment could be an upper bound estimate of the capacity of a structure, if out-of-plane mechanisms are excluded which may be the case of existing historical masonry structures. The current paper examines results of macro-element based modelling and analysis with that from a micro-modelling approach, particularly in terms of the global capacity and damage and collapse mechanisms. The paper concludes with a word of caution on the use of macro-element modelling approaches for seismic assessment of existing masonry structures, particularly where out-of-plane mechanisms can be expected and rigid diaphragm action is not guaranteed.

Complex dry stack stone corbel-vaulted structures are commonly constructed as assemblages of several corbelled sub-systems. While there is enough architectural documentation, limited studies explore their structural stability or factors affecting it considering that they are rather susceptible to support disturbances. A systematic study of the influence of geometry (global level), interactions between adjacent units (intermediate level) and material strength parameters, particularly joint friction (local level) on their stability is warranted. A series of static experiments are conducted on a 1:3 scaled model of an existing corbelled vault to various support movements replicating lateral actions caused by seismic or differential support movements, with non-contact measurements based on photogrammetry. Sensitivity to joint roughness and moisture conditions is also examined. Failure mechanisms categorized as overturning, joint sliding, or a combination of overturning and sliding, provide an insight on the redundancies available in complex-vaulted systems, and the interplay between one mechanism over another. The possibility of estimating collapse displacement or rotation using graphical methods in predominant overturning or the combination failure mechanism is discussed. In predominant sliding failure mechanism, a simple method to assess safety is explained with the use of the friction cone concept when subjected to known input forces.

The presidential palace of India was constructed between the years 1912 to 1929 CE in a novel architectural style resulting from an amalgamation of Colonial and traditional Indian styles. During a visual inspection of this double-domed structure, meridional cracks were spotted in two out of the four niches in the drum of the lower dome. The observed distress raised two important issues that needed to be resolved- the cause of the cracks and their impact on the structural response. The uncertainty in the actual geometry of the building and the variety of materials used in its construction, the complex layout, lack of prior knowledge of reinforcement details and the undocumented changes made to the structure prompted the adoption of a multi-disciplinary scientific investigation to evaluate the structure. The methodical approach encompassed a literature review of dome failures in the past, historical and geometrical surveys, foundation inspection and the use of relevant non-destructive and minor destructive tests in the evaluation of the superstructure. The information gained from the aforementioned investigation was useful in the development of a 3D finite element model of the structure. The findings of the investigation revealed that owing to its geometry, tensile stresses develop in the unreinforced brick masonry drum. The reduction in the thickness of the drum at the locations of the niches results in an inherent weakness in the structure. The opening for the stairwell in the north-eastern corner of the building, at the level of the drum, further reduces the tensile resistance of the abutment system of the dome and gives rise to the observed crack pattern

A quantitative, rapid screening assessment methodology for masonry arch bridges, with minimal input parameters, is proposed. The developed mechanism-based analysis procedure is validated against a set of available experimental data. Performance levels are then prescribed for bridges falling into proposed subsets based on geometric proportions. A generalized amplification factor (κ) is introduced, which could account for an increase in demand due to a dynamic vehicle-bridge interaction as well as an increase in axle loads. Finally, fragility curves are generated, which gives the probability of collapse for a bridge subset against increasing demand parameter.