Claudia Casapulla

Archaeological consolidation of UNESCO masonry structures in Oman: the Sumhuram Citadel of Khor Rori and the Al Balid Fortress

A series of missions, starting from early 2005 up to 2009, have been managed to restore the ancient city walls of Sumhuram(4th century bc to 6th century ad) in the site of Khor Rori, with a group of archaeologists of the University of Pisa. Also, from early 2007, a series of missions have been managed to consolidate the dry masonry Fortress in UNESCO site of Al Balid erected circa 1100 ad with archaeologists of the University of Missouri. Both sites are located in the area of Salalah in southern part of the Sultanate of Oman. The sequence of dry season and rainy season during the Khareef period (Monsoon phenomena) caused several collapses on the excavated masonry structures, with risks for safety of visitors and archaeologists. The walls of Sumhuram, affected by the loss of connection between the two limestone masonry faces, have been rebuilt with the original texture of bricks using a new mix design for mortar joints with the same colors, consistency, and proper strength and durability. The safety level of the consolidation works is evaluated by observing on site the shape of the collapse surfaces and using the classical limit analysis approach. The collapses of Al Balid dry masonry walls have been originated by the loss of permeability of the external wall faces due to the progressive filling of joint by soil. Consolidation activities consisted of rebuilding with the same blocks down and substituting the earth behind the external layers with gravel and high permeability filling. An analytical model of dry rigid block masonry with frictional interfaces has been used to represent the out-of-plane behavior, in order to define the maximum height of excavation and the maximum free height of the restored walls to guarantee safety for workers.

EXPERIMENTAL VALIDATION OF IN-PLANE FRICTIONAL RESISTANCES IN DRY BLOCK MASONRY WALLS

This paper presents the experimental and analytical validation of the lateral strength of dry block masonry walls under in-plane loading. The analytical evaluation of the in-plane frictional resistances activated at the onset of the rocking-sliding mechanisms is revisited in order to account for the different contributions of the self weight of the wall and additional loads. It is assumed that the wall is arranged in a running bond pattern, with rigid blocks and dry contact interfaces governed by cohesionless Coulomb failure criterion. The accuracy and robustness of the analytical results are assessed by experimentally testing both the resultant frictional resistances and their applications points. Both pure sliding and rocking-sliding failure modes are simulated with a testing device designed and realized ad hoc (no standard equipments and procedures were found in the literature). A good agreement between the analytical and experimental results is shown for the selected cases. 2607 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2607-2618

ROCKING RESONANCE CONDITIONS OF LARGE AND SLENDER RIGID BLOCKS UNDER THE INTENSE PHASE OF AN EARTHQUAKE

A simplified approach is proposed in this paper for assessing the safety levels of the seismic response of large and slender rigid masonry blocks. The dynamic behavior of rigid free-standing blocks subjected to earthquake ground motions is highly non-linear and sensitive to small perturbations of various parameters. Many difficulties arise in defining reliable response spectra for such systems and these are well known in the literature. An artificial limit accelerogram is herein proposed to represent the most unfavorable effects of the intense phase of an earthquake. This consists of a sequence of instantaneous impulses, all applied right after the impact of the blocks on the ground. The resonance conditions also aim at highlighting to what extent the ground motion details and the system parameters can influence the rocking response. A secondary sequence of intermediate impulses is then introduced to reduce the resonance effects and to cover a broad range of conditions. Approximate equations of motion of the rocking blocks are also proposed and numerical analyses are performed to highlight the most significant aspects of the proposed approach. 2867 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2867-2878

A simplified procedure for the seismic safety of large and slender rigid masonry blocks

This paper aims at finding the features of an artificial accelerogram which can be used to assess the seismic safety of large and slender rigid masonry blocks. The most important feature derives from a simple observation: well-known uncertainties on time variations of seismic actions imply that seismic risks analyses must be developed without privileging any detailed description of expected accelerograms. It follows that the best choice to build an artificial accelerogram is to represent it with sequences of instantaneous Dirac impulses and to look at its worst effects. A multiple impulse input is herein proposed, with impulses all applied right after the impact of the generic block on the ground. Intermediate impulses are then introduced to reduce the resonance effects and to cover a broad range of conditions. Approximate equations of block motion are proposed and numerical analyses are performed to highlight the most significant aspects of the proposed approach.

Seismic safety assessment of a masonry building according to Italian Guidelines on Cultural Heritage: simplified mechanical-based approach and pushover analysis

The seismic safety assessment of a case study of a masonry building located in Naples (Italy) was performed together with a critical appraisal of the methods used. Being built before the introduction of proper seismic code provisions, this unreinforced masonry building could be representative of many other vulnerable historic buildings in earthquake-prone urban areas. First, a simplified model of the global seismic response was analyzed according to the LV1 assessment level provided by the Italian Guidelines on Cultural Heritage. The results obtained using old and updated versions of these guidelines were compared. A good agreement was revealed with reference to the detection of the weaker direction and the prevailing failure mechanism, but some differences were found about the calculation of the base shear capacity and the corresponding ground acceleration. Then, the achieved results were compared with those obtained using a more refined approach of nonlinear static analysis according to the LV3 assessment level. The results were reported in terms of damage and collapse mechanisms of masonry walls, pushover curves and seismic safety indexes. A further comparison was carried out between the model with flexible horizontal structures and that with the assumption of all the floor diaphragms as completely rigid. Although the two assessment methods LV1 and LV3 are not alternative to each other, since belonging to two different levels of evaluation, some critical issues were addressed in order to derive useful information on the reliability and the limits of validity of the simplified mechanical model, characterized by a force-based approach.

NON-LINEAR KINEMATIC ANALYSIS OF MASONRY WALLS OUT-OF-PLANE LOADED. THE COMPARATIVE ROLE OF FRICTION BETWEEN INTERLOCKED WALLS

In this paper the limit analysis of a simple out-of-plane failure mechanism of a laterally weakly connected masonry wall involving frictional resistances is developed according to the displacement-based approach. The pushover analysis is made considering geometric nonlinearity, i.e. by evaluating the static multiplier for varied kinematic configurations, as a function of the displacement of a control point. The effect of the interlocking between the front wall and the sidewalls gradually decreases after a certain displacement, due to the progressive detachment of the front wall and the variation of the frictional resistances can be represented by a non-linear function of the decreasing number of involved rows. The stabilizing role of friction between interlocked walls is compared to another system of strength in masonry buildings, i.e. the effect of tie-rods, with and without the detrimental effect of the static thrust of masonry vaults. The sensitivity of the load multiplier to these strength parameters is investigated with reference to different combinations of loading conditions. Comparative results and pushover curves are developed to evaluate the displacement capacities for each case analyzed. Claudia Casapulla and Luca U. Argiento

Experimental and Analytical Investigation on the Corner Failure in Masonry Buildings: Interaction between Rocking-Sliding and Horizontal Flexure

ABSTRACT The failure mechanism of corners in masonry buildings has frequently been observed in seismic scenarios, but only a few works and no experimental investigations devoted to it are available in the literature. In this aritcle, the experimental behavior of a simple masonry corner is first analyzed, by simulating the seismic horizontal actions through a progressive tilting of the supporting base. Then, the conditions of the onset of two possible failure modes are analytically formulated: they are the rocking-sliding and the horizontal flexure mechanism. A three-dimensional macro-block model with frictional joints is used to analyze these mechanisms, while the crack patterns and the load factors are derived through the kinematic approach of the limit analysis. The evaluation of the in-plane frictional resistances involved by the rocking-sliding mechanism is performed by applying a reliable criterion previously proposed, while for the torsion strength involved in the horizontal flexure mechanism, simplified yield conditions are adopted and a possible criterion is also introduced to take into account the actual reduction of the contact surfaces. Last, the experimental findings are compared and critically interpreted in light of the analytical results and the influence of the main parameters on the prevailing mechanism is highlighted.