Rubble Core Research Articles

Effect of the vertical component of ground motion on a rubble masonry wall model

In this paper the influence of the vertical component of ground motion on the performance of an unreinforced masonry wall is analysed using sets of one-component and two-component ground motions. The set of motions represents the actual seismicity of L'Aquila, while the investigated wall mimics an experimental specimen with two unconnected external leaves and a rubble core. The model falls within the mixed finite element method – discrete element method and accounts for crack formation, complete separation and new contact formation. The modelling strategy is capable to simulate the out-of-plane seismic response and the progressive loss of compactness of the wall up to collapse with the separation between the two external leaves. The vertical component increases the fragility of the wall and confirms the relevance of vertical ground motion for very vulnerable constructions. Nonetheless, to worsen the response, the vertical component needs to overcome specific, non-negligible intensity measure thresholds.

Hygrothermal modelling of historic rubble masonry walls: Accounting for geometric and compositional variability

An established issue when assessing the hygrothermal performance of heritage buildings is the correlation between measured data and model outputs. This can be attributed to many factors including climate data and hygrothermal material property data. Two overlooked factors are the variation in geometry and level of decay in the structure. This can be true for several historic wall assemblies with irregular geometries and elevated levels of decay. There is a lack of guidance on how and when to incorporate this into a hygrothermal model. The goal of this paper is to examine how this variability in geometry and composition may affect model outcomes using a simulation approach with stochastic methods for a sample rubble core masonry wall.Geometrically stochastic models were generated from a script accounting for varying levels of air voids in the wall and irregular stone patterns. The presence of voids alters heat, capillary and vapour transport. This was combined with hygrothermally dissimilar mortar and stone units. Simulations were performed under four boundary conditions: heat, drying, wetting and actual weather data. The results showed that geometric stochasticity can lead to a large variation of results. The presence of voids in the wall also led to a reduction in heat and moisture transport in the assemblies. The results of the stochastic simulations were then compared to a set of simplified one and two-dimensional models to judge their appropriateness. It was found that 2-D parallel like models that account for the mortar joint in some fashion are most appropriate.

Seismic stability assessment of an ancient dry stone defensive wall

This paper presents a sophisticated numerical investigation of the seismic stability of a ruinous section of the city walls of ancient Messene (Peloponnese, Greece), which has been recently proposed to be partially but extensively restored. The examined structure corresponds to the proposed restoration. 3-D numerical analyses were performed using the FE software Abaqus and records of four earthquakes suitably scaled. The analyses included, among others, an investigation of the influence of the monument’s rubble core on its seismic response. The numerical results showed that if the monument presents, after its restoration, all the basic conditions favourable for its stability (i.e. solid base, practically vertical outer and inner masonry faces, intact or restored stone-blocks in good contact, gradual formation of the courses at the ends of the masonry faces), it will withstand seismic actions of equal or higher levels than the ones the Seismic Code imposes for the design of the new buildings in the area. Furthermore, the results indicated that as much as the restoration expands (leading for the structure to be closer to its complete, original form), so much higher the seismic stability of the monument will be, provided that the aforementioned conditions will still apply.

ORPHAN BREAKWATERS: COLLAPSE AND TRANSMISSION REDUCTION

In the past, many coastal towns or villages constructed harbours for trade and/or fishing. These were protected by breakwaters, commonly rubble mounds to low-water, surmounted by vertical walls of dressed stone blocks (later concrete) with rubble core. Now, 100-150 years later, many such harbours have little or no income to maintain or repair their breakwaters, but meantime, the areas protected have been adopted for commercial and residential purposes, at increased risk of flooding if the 'orphan' breakwater were to collapse, Hampshire et al. (2013). Even after collapse, some wave reduction will however still be afforded by the relict structure. Tests by Allsop et al (2017) have modelled the collapse of several simplified breakwaters, and measured levels of wave transmission over the collapsed structures. This paper extends that work with more analysis of collapsed crest levels, and hence of likely wave transmission.

Assessment of Multi-Wythe Stone Masonry Subjected to Seismic Hazards

Heritage stone buildings are typically vulnerable to seismic events. Results of an experimental program were analyzed to evaluate the shear strength and intrinsic damping of stone masonry representative of the West Block of the Canadian Parliamentary Precinct in Ottawa. Eight representative wall specimens with different rehabilitation schemes had been tested under different static and dynamic loadings. Each wall had wythes of sandstone and limestone connected by a rubble core. The results show the shear strength of the walls could be predicted accurately and that no strengthening scheme was particularly beneficial. The effective viscous damping ratios varied between 7 and 9%.

Discrete Element Modeling of Stone Masonry Walls With Varying Core Conditions: Prince of Wales Fort Case Study

The Prince of Wales Fort was constructed in the 18th century as a Vauban style stone masonry fortification where the Churchill River flows into Hudson’s Bay, across the river from Churchill, Manitoba, Canada. Since completion the fort has been exposed to harsh weather conditions, which have led to significant deterioration and deformations in the walls, with some cases of localized collapse. Recently, an increase in the rate of degradation has made preventative conservation an issue of interest. For this conservation to be possible, an understanding of the cause of failure of the walls is first required. Discrete element modeling (DEM) using the non-smooth contact dynamics (NSCD) method utilized in the Program LMGC90 has been used as a first step in understanding the failure mechanism of the wall system. The results of the modeling show that the rubble core of the walls can transition from stability to instability as the cohesion between the stones is altered. Grouting the core will alter the bond between stones, increasing the stability of the core, and is thus one possible conservation method.

On the Dynamic Behaviour of Strengthened Stone Masonry Walls

Unreinforced stone masonry is common in heritage structures worldwide. Unfortunately, these structures are susceptible to failure or severe damage when subject to dynamic or seismic loading. Conservation of historic structures is a challenge as the heritage and cultural values need to be preserved while the advent of new seismic codes may require major strengthening to be implemented. The new seismic codes demand high seismic strength and ductility for such structures, whereas neither the strength nor the ductility of an existing stone masonry building can be quantified easily. The Parliament buildings of Canada fall into this category. Therefore, an extensive experimental program was carried out to investigate the dynamic and seismic behaviours of stone walls representative of Canada’s Parliament buildings. The walls were constructed of double stone wythes with the cavity between being filled with weak mortar, shards and small stones, constituting a rubble core of the walls. The experimental program included in-plane quasi-static, free vibration and high frequency loadings, together with out-of-plane shake table tests. The tests were aimed at investigating the integrity, strength, damping, stiffness degradation, and ductility of the walls. Different potential strengthening methods were assessed, methods that would minimize structural intervention and preserve the heritage values of the building. The methods involved different metallic anchors and traditional stone interlocking to tie the two outer wythes together. Fortunately, the stone walls exhibited satisfactory performance in all cases. In addition, the test results suggested that plain un-strengthened stone walls had strength and other characteristics similar to those of the rehabilitated walls, in the range of the imposed load scenarios.

Damping mechanisms and damping ratios in vibrating unreinforced stone masonry

In seeking to understand the dynamic behaviour of historic stone structures, eight representative walls were constructed and tested under in-plane free vibration conditions. Each wall consisted of two wythes, one sandstone, one limestone, joined by a rubble core of small stones and mortar. The walls were 2.0 m wide by 2.75 m high by 0.54 m thick. The free vibration tests were conducted in the wall’s in-plane direction at three levels of damage: the first was the undamaged state of the walls, the second after in-plane damage, and the third was after both in- and out-of-plane testing. As such, dynamic characteristics such as effective damping mechanisms and ratios and the natural period of vibration could be evaluated. It was found that although viscous damping was dominant, Coulomb friction damping had significant influence on wall vibration. The viscous damping ratio was 0.03 for the undamaged walls and increased with damage.

In-plane seismic behaviour of historic stone masonry

Since the advent of the latest National building code of Canada, the level of intervention required to meet seismic requirements for the rehabilitation of heritage buildings has increased significantly. An example of this type of project is the rehabilitation of the West Block on Parliament Hill in Ottawa. Eight walls representative of the stone masonry in the West Block building were constructed, some with different rehabilitation schemes, and tested to investigate their in-plane seismic behaviour. The walls were double wythes of sandstone and limestone connected by a rubble core. The walls were 2750 mm high by 2000 mm wide by 540 mm thick. The rehabilitation schemes represented different ways of tying the stone wythes together, since the outer sandstone wythe has separated from the rubble core in some locations in the existing structure. The results reveal that the suggested strengthening schemes neither benefit nor degrade the in-plane seismic behaviour compared to that of a plain wall.

Ground penetrating radar investigations for the restoration of historic buildings: the case study of the Collemaggio Basilica (L’Aquila, Italy)

Ground penetrating radar (GPR) surveys were applied in the preliminary stage of a project of structural monitoring and restoration of the facade of the Collemaggio Basilica, a medieval church located in L’Aquila (central Italy). GPR surveys were very useful in evaluating the state of conservation of the facade and in identifying the thickness of its walls, the forms and deterioration of its masonry with its ashlar facing and rubble core, and the forms and locations of its middle cornice supports. GPR was demonstrated to be an ideal non-destructive method to investigate ancient structures of high cultural and historical value.

Application of impact-echo technique in diagnoses and repair of stone masonry structures

The impact-echo technique is traditionally used to determine position of intermediate and large defects within concrete structures. In this paper, application of the impact-echo technique for assessment of bonding condition between the facing stones, mortar, and inner rubble core in stone masonry structures is discussed. In addition, results of field testing on a historic Canadian stone masonry building is presented, which illustrates the capabilities of an impact-echo system to help with evaluating the structural stability of critical components, particularly the bonding conditions and presence of voids and cavities.

The Fortified Hill Site Near Gila Bend, Arizona

ABSTRACTExcavations arc reported of an unusual site, located on top of a volcanic escarpment, on the Gila Bend Indian Reservation. The rooms and walls were reconstructed during excavation. All components, with the exception of probable ceremonial units, were composed of rubble core masonry. Three building phases were delineated. Rooms were grouped in social units of two or three houses.Two burial zones of primary cremations were found. Mining areas were evident under the edge of the site and on a neighboring escarpment. Tests indicate that minerals were mined for ceramic temper or obsidian.The cultural assemblage is a manifestation of the Tanque Verde phase (ca. A.D. 1200–1300) as known from the Tucson Basin.It is proposed that the village was settled by migrants to the area after it was abandoned by the Hohokam proper. Site location, on a cultural frontier, makes it possible but not certain that the defensible quality of the hill was of prime concern.

Cannon-Manufacture at Pippingford, Sussex: The Excavation of Two Iron Furnaces ofc.1717

Two blast furnaces produced iron at Pippingford Park, Sussex (TQ/4503l6) in the early 18th century. At the first to be built (the west furnace) guns were cast; this was excavated in 1974, although its surroundings remain to be explored. A boring mill was sited close to the east furnace, the wheels of the boring carriage being in situ on their tracks. The east furnace was construded during the life of the west site, and the surviving casting beds showed that pig iron had been produced. Robbing of stone had been severe in the case of the east furnace, in contrast to its predecessor, whose rubble core survived 1–1.5 m. in height, and whose gun-casting pit was in good order.

TIMBER-LACED AND VITRIFIED WALLS IN IRON AGE FORTS: CAUSES OF VITRIFICATION

been set out more than once . The practical demonstration in 1937 by Professor V. G. Childe that a drystone wall with many timber beams inside its rubble core would, if burnt under the right conditions, produce vitrified masses, provided the first really satisfactory explanation of the phenomenon*3 >. Forts with such timber-laced walls are known from the continent and there are a few in Scotland of which the best known is probably Aber nethy in Perthshire*4 >. The theory that vitri fication was a deliberate process undertaken to create a fused rampart of enormous strength, always improbable and lacking any experi mental support, finally became untenable after this experiment. However, a conclusive demonstration of the correctness or otherwise of this theory of the origin of the vitrified forts is hard to find because, while beam-holes remain in unburnt timber-laced walls as at Aberncthy, the pro cess of vitrification usually completely destroys the masonry and causes built wall-faces to collapse, together with any beam-holes in them. Finavon is a good example of this. Even the surviving inner wall-faces are so badly warped that, though there are sometimes suggestions of beam-holes, nothing conclusive is visible(5>. Excavations on the vitrified fort of Dun Lagaidh in Wester Ross in August 1967 uncovered a short stretch of wall standing 6 feet high with both vitrified core and beam holes visible (Pl. i). The wall was in fact an outwork, protecting the eastern end of the oblong hillfort<6) : a mass of fused rubble had burst from the core through the inner face which, since it was still standing vertical, must previously have been buried by collapsing rubble from the upper parts of the wall before the maximum heat had been generated. Two rows of clear beam-holes are visible next to this. This is a conclusive demonstration that Childe's theory is correct and that masses of vitrified rubble are the remains of burnt