EP3040497A1

EP3040497A1 - Antiseismic masonry infill

Info

Publication number: EP3040497A1
Application number: EP15203213.2A
Authority: EP
Inventors: Guido MAGENES; Paolo MORANDI; Riccardo Raimondo MILANESI
Original assignee: Associazione Nazionale Degli Industriali Dei Laterizi; Associazione Naz Degli Ind Dei Laterizi
Current assignee: Associazione Nazionale Degli Industriali Dei Laterizi; Associazione Naz Degli Ind Dei Laterizi
Priority date: 2014-12-30
Filing date: 2015-12-30
Publication date: 2016-07-06
Anticipated expiration: 2035-12-30
Also published as: EP3040497B1

Abstract

An earthquake-proof masonry infill wall is described which comprises a series of superimposed masonry strips (7). Each masonry strip (7) comprises a plurality of blocks, that is masonry elements (8), arranged adjacent and horizontally such to occupy a space between two columns (3) of the framed structure (2). A sliding element (10) interposed between two adjacent masonry strips (7) has opposing section bar elements (11) that allow a masonry strip to slide in a guided manner with respect to another masonry strip in case of a movement of the infill wall.

Description

The work that has led to this invention has taken advantage of a funding of the European Union Seventh Framework Programme (FP 7/2007-2013) under grant agreement n. 606229.

TECHNICAL FIELD

The present invention relates to the field of devices and systems for limiting the damage of structures subjected to seismic actions.
In particular the invention relates to a masonry infill wall in buildings with wall, framed or mixed structure, able to limit the damage of the masonry panel and of the adjacent structural elements when subjected to seismic actions.
Generally the invention relates to an infill wall according to the preamble of claim 1.

PRIOR ART

The most common type of infill wall is a masonry infill wall completely adhering to the frame adjacent thereto. The masonry is constructed without disconnections and it is in contact with the structural elements.
The conventional infill wall solution can have many variants: it can be composed of a single-layer or a double-layer masonry (often the two faces are not connected with each other) and it can be composed of types of masonry made of different materials (e.g. with blocks made of clay or concrete) with blocks with different holes (e.g. solid blocks, or perforated blocks, with vertical or horizontal holes) and with different types of mortar joints (thin or conventional horizontal joint, conventional vertical joint or with pocket or dry and groove and tongue joint).
Conventional infill wall has been the subject matter of studies all around the world since many decades, however scientific and professional communities have not come to an agreement on how solving the problems deriving from its use in case of seismic events. Although such conventional constructional solution, in its several variants, has some advantages such as the easiness in construction and its cheapness, after experimental searches and after post-seismic event inspections on site, several drawbacks have been identified related to such type of infill wall.
Some of the drawbacks of adhering infill walls are the high seismic vulnerability when subjected both to actions in the plane of the wall and to actions perpendicular thereto. Deep in-plane damages can occur in the infill wall, with cracks involving both the blocks and the mortar, already at low storey drift levels (the more brittle the type of masonry is the lower they are) with the consequent risk of having failures and partial collapses of the masonry for high displacement levels.
Another drawback of conventional solutions is the interaction between the frame and the infill wall, which often is the reason of failure due to local crushing at the corners of the infill wall or the reason of increase in the action shearing the adjacent column made of reinforced concrete, with possible brittle fractures due to shearing the structural element, in particular in presence of strong infill walls (with a high thickness). The generation of a diagonal strut mechanism produced by the infill wall further leads to a change in the distribution of shear and moment on the columns due to the contact locally occurring between the strut and the columns of the frame.
The out-of-plane collapse mechanisms are a further drawback related to conventional infill walls. Currently the strong infill walls having a high thickness are a common solution to face the requirements of the regulations in the field of thermal-acoustic insulation; they have exhibited a good behavior in terms of out-of-plane strength, even if they considerably enhance in-plane drawbacks mentioned above.
The double-layer infill walls not connected with each other on the contrary do not guarantee a suitable strength and stability against out-of-plane actions: a collapse mechanism due to out-of-plane ejection of one of the masonry layers has often been experienced.
A further drawback caused by the presence of masonry infill walls adhering to the frame takes place with reference to the general response of the whole building, since the seismic behavior of the structure is substantially modified. Such changes with respect to the "bare" structure (that is with no infill walls) lead to lose the real structural response since it is difficult to design infilled buildings considering the influence of the masonry panels in the calculation model (at least in terms of strength and stiffness).
The lack in the control of the real structural response, associated with the presence of adhering infill walls, can cause "soft storey" mechanisms or plan torsion effects in case of infill walls placed in an irregular manner in plan and in elevation, effects that are particularly critical when a structure is subjected to seismic actions.
One of the solutions used for overcoming the problem of the excessive in-plane brittleness and out-of-plane vulnerability of conventional infill walls is to reinforce them by inserting vertical and/or horizontal reinforcements inside the infill wall, or suitable meshes of several types and materials (e.g. metal meshes with small diameter). The reinforcements can also be made of composite materials (e.g. carbon fibers).
Such solutions can lead to an increase in in-plane and out-of-plane strength, stiffness, and sometimes in deformation capacity; however these "improved" solutions do not systematically solve some of the drawbacks mentioned above, particularly those involving infill wall-frame local interaction and the consequent possible shear failure/collapse of the structural element, the impossibility of predicting the change in the structure properties and the irregularity in the distribution of the masonry panels in plan and/or in elevation.
Another system used in the current construction approach, aiming at reducing the problems related to frame-infill wall interaction and those related to the change in the seismic behavior of the structure, is to create a space ("gap") between the infill wall and the confinement frame; however the out-of-plane stability would be drastically compromised, above all if suitable overturning prevention systems are not designed. The solutions with the "gap" could exhibit problems of local failures if subjected to dynamic actions: when the frame reaches such deformations to close the "gap" impulsive impacts could be generated with the risk of having deep and uncontrollable damages to the infill wall; moreover there would be the problem related to the type of material to be inserted in the gap able to face thermal-acoustic insulation and fire resistance problems.
From the Japanese patent JP H 02 164984 by Fujita Corp., a masonry wall is known comprising masonry blocks having transverse holes where a vertically developed joint made of lead (or an alloy thereof) is inserted. The two ends of the joint are therefore housed in respective holes of two superimposed blocks and they contain their relative movement by absorbing the oscillations deriving from earthquakes.

OBJECTS AND SUMMARY OF THE INVENTION

It is the object of the present invention to overcome the prior art drawbacks.
Particularly it is an object of the present invention to provide masonry infill walls whose construction characteristics allow the drawbacks mentioned above to be solved in a simple and cheap manner.
Moreover it is an object of the present invention to decrease the seismic vulnerability of a structure provided with masonry infill walls.
Another object of the present invention is to limit both local interactions and the interactions due to in-plane deformations, of a masonry infill wall with the columns of a frame housing such infill wall.
A further object of the present invention is to guarantee the strength of a masonry infill wall when subjected to out-of-plane stresses.
Finally it is also an object of the present invention to provide a infill wall allowing the general response on the whole structure to be controlled as it is similar to that calculated by the designers on a "bare" structural model (with no infill walls).
These and other objects of the present invention are achieved by a masonry infill wall embodying the characteristics of the annexed claims, since they are an integral part of the present description.
The present invention relates to a masonry infill wall intended to be provided inside buildings with a framed, wall or mixed structure, able to limit the damage of the masonry panel and of the adjacent structural elements when subjected to seismic actions.
The masonry infill wall comprises a series of superimposed masonry strips intended to be received in a space defined by the structure frame. Each masonry strip comprises a plurality of (preferably at least three) courses of blocks, for example clay blocks, arranged adjacent and horizontally. Besides the blocks and the mortar composing the masonry part of the infill wall, the latter comprises sliding elements interposed between two superimposed masonry strips. Each sliding element comprises two section bar elements allowing a masonry strip to slide in a guided manner with respect to the other one in case of seismic movement of the structure.
The infill wall further comprises a vertical joint element, provided with a shear key, intended to be inserted into a seat provided at one end of the infill wall and obtained in a special block of the plurality of blocks such to allow the shear key to slide in the seat in case the infill wall is subjected to stresses.
Such solution allows the formation of cracks on the blocks and on the mortar used for the infill wall to be reduced and therefore the risk of failure or partial collapse of the infill wall to be reduced, both in the case of events of medium-low intensity and in the case of important seismic events. The relative motion between the masonry strips, made possible by the presence of the sliding element, reduces the risk of creating a compressed strut that, by diagonally passing through the whole infill wall, can cause serious damages both to the masonry and to the structure itself. Accordingly, in case of seismic stress, the formation of cracks is concentrated only at the section bar elements of the sliding element and the damage to the masonry strips is considerably reduced. Such solution therefore aims at reducing the seismic vulnerability of a masonry infill wall.
In addition such solution guarantees the out-of-plane strength of the infill wall by the shear keys, constrained to the columns and blocks with a recess able to withstand the local shear. The flexural strength of the masonry strip prevents the out-of-plane failure thereof.
Advantageously the infill wall further comprises an interface mortar intended to be interposed between the infill wall and one or more elements of the framed structure. The interface mortar has values of the Young's modulus preferably ranging from 100 to 150 MPa and compressive and flexural strength values higher than 4MPa and 2Mpa respectively; this allows the local interaction between the infill wall and the frame to be limited thus reducing concentrations of forces that can cause local failures in the masonry and in the structural elements.
The invention relates also to a method for producing an infill wall as denoted above and as better described in the description below.
Further objects and advantages of the present invention will be more clear from the following description and from the annexed claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below with reference to non-limiting examples, provided by way of example and not as a limitation in the annexed drawings. These drawings show different aspects and embodiments of the present invention and, where appropriate, reference numerals showing like structures, components, materials and/or elements in different figures are denoted by like reference numerals.

Figure 1 is a front view of a masonry infill wall allowing the seismic stress-derived damage thereof and of the structure where it is inserted to be limited and controlled.
Figure 2 is a vertical sectional view of the infill wall of figure 1.
Figure 3 is a horizontal sectional view of the infill wall of figure 1.
Figure 4 is a cross-section view of a detail of the infill wall of figure 1.
Figure 5 is a perspective view of a detail of the infill wall of figure 1.

DETAILED DESCRIPTION OF THE INVENTION

While the invention is susceptible of various modifications and alternative forms, some preferred non-limitative embodiments, provided by way of example, are described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific embodiments disclosed, but, on the contrary, the intention of the invention is to cover all modifications, alternative constructions and equivalents falling within the scope of the invention as defined in the claims.
Therefore, in the description below, the use of "for example", "etc", "or" indicates non-exclusive alternatives without limitation unless otherwise defined; the use of "also" means "among which, but not limited to", unless otherwise defined; the use of "include/comprise" means "include/comprise, but not limited to," unless otherwise defined.
In the present description the term block means a masonry element.
Figure 1 shows a front view of a masonry infill wall 6 that allows seismic stress-derived damage thereof and of the structure 1 where it is inserted to be limited and controlled.
The frame 2 of the structure comprises a base 5 and two columns 3 intended to support a beam 4, thus defining a space wherein a masonry infill wall 6 is provided.
The infill wall 6 comprises a plurality of masonry strips 7 that are superimposed and housed within the frame 2. The masonry strips extend for a length I equal to the distance between the two columns 3 and for a height equal to the distance between the beam 4 and the base 5. Each masonry strip comprises at least three courses of clay blocks 8, wherein the blocks are arranged adjacent to each other and in the horizontal direction for the whole length l of the infill wall 6. Preferably the blocks 8 are made of clay material by using a strong single-layer structure, such to reduce, in a manner known per se, the risk of any type of local damage and therefore such to provide a resistance to a lateral compression that is high enough to withstand the horizontal force developing inside each masonry strip during a seismic event.
A binding material 9, for example a mortar for building use, bind together the blocks 8 of each masonry strip 7.
Since each masonry strip can comprise several courses of blocks, the binding material in such case acts for binding together the superimposed courses of each masonry strip.
The infill wall further comprises a sliding element 10 interposed between two superimposed masonry strips. Such sliding element 10 comprises section bar elements 11 facing with each other and allow a relative sliding between one and another masonry strip when the infill wall is subjected to lateral stresses. Inside the infill wall 6 therefore there can be a series of masonry strips separated from each other by a sliding element 10 able to allow them to accomplish a relative sliding.
In the embodiment shown herein, the sliding element 10 is composed of two section bar elements 11 (well visible in figure 4) constrained to the opposite faces of the two masonry strips 7.
The two section bar elements 11 are made of polymer material with good mechanical properties and a low coefficient of friction, preferably made of polyamide 6 with molybdenum disulfide (PA 6 + MoS2). Even if the solution is less advantageous, however it is possible to made the sliding element 10 of other types of materials, such as for example steel.
In the example considered herein, the two sliding elements have a corrugated profile, seen in a plane transverse to the development plane of the sliding surface. Such choice allows the sliding of the opposite masonry surfaces to be guided along the direction of development of the masonry surfaces, that is in the horizontal direction from one to the other column and moreover it provides a suitable mechanical interlock for actions perpendicular to the longitudinal development of the wall. As an alternative however it is possible to provide other shapes, not necessarily combined, even if such last characteristic is preferable.
The sliding elements 11 are caused to adhere and to be fastened to the masonry strips 7 by using a material that, in the example of figure 4, is the same binding material 9 used for fastening together the blocks 8 of the masonry strips.
In the preferred embodiment described here, the infill wall 6 comprises a joining element 13 (visible in figure 3) interposed between the masonry wall of the infill wall and the columns.
The junction element 13 comprises a shear key 130 intended to be inserted in a seat 81 provided at the end of the masonry wall and obtained in a special block (80).
Such as seen in figure 5, in such embodiment the shear key 130 is made of an "omega" shaped section bar element. The shear key is preferably made of steel and it is engaged with the column through nails, for example being shot by a nail gun in a simple and quick manner.
The infill wall made in this way provides the courses of clay blocks of the masonry strips to comprise at least one end block 80, adjacent to the column, shaped in such a manner to form a seat 81 intended to house the shear key 130.
The block 80 is dimensioned to guarantee such a local shear strength to allow each masonry strip 7 to transfer the shear forces generated by a seismic action out-of-plane, that is directed transverse to the infill wall 6.
Between the seat 81 and the shear key 130 there is provided a mortar 14, visible in figure 5, intended to limit the interaction of the infill wall 6 with the frame 2, due to such reason it is preferably used also between the beam 4 and the masonry of the infill wall.
The mortar 14 has values of the Young's modulus ranging preferably from 100 to 150 MPa and it has values of compressive and flexural strength higher than 4MP and 2 MPa respectively.
The infill wall 6 further comprises a plaster layer 15 laid on both the faces of the infill wall 6 for the whole length l. Such layer has such tensile and flexural strength values to guarantee a possible horizontal flexural strength to seismic actions acting out-of-plane on the masonry strips. Preferably such tensile and flexural strength values are selected such to allow the masonry strip to withstand an acceleration up to 3g.
Therefore it is clear, for a person skilled in the art, that it is possible to make changes and modifications to the solution described with reference to the figures shown above without for this reason departing from the scope of protection of the present patent as defined in the annexed claims.
For example the use of the plaster 15 can be replaced by conventional plasters where a suitably dimensioned appropriate mesh made of glass fibers or any other material is inserted.
Moreover the shear key 130 and the recessed block 80 can have different shapes depending on the thickness of the wall and on the required out-of-plane seismic action.
The infill wall 6 can vary in thickness and type; a main aspect that has to be guaranteed is the lateral compressive strength (in the plane of the wall) of the masonry and the block stiffness. As a consequence of the thickness of the infill wall the dimensions of all the elements present in the innovative infill wall can change (sliding joint, interface mortar, shear key, ...).
Although in the embodiments described above the sliding element 10 has been described as an element separated from the clay blocks 8, in one embodiment, even if less performing, at least one section bar element 11 of the sliding element 10 is made as one piece with the clay blocks 8 of a masonry strip 7.
Moreover although in the embodiments described above the masonry strips comprise courses of clay blocks 8, it has to be intended that there is no intention to limit the invention to such specific embodiment since the masonry strips can comprise masonry blocks made of a material different from clay, such as for example concrete blocks, particularly vibration-compressed concrete (with heavy and light aggregates) and/or autoclaved aerated concrete (AAC), blocks made of stone particularly agglomerate and/or natural stone, cement blocks or also blocks of calcium silicate.
Therefore generally the masonry infill wall comprises:

a plurality of superimposed masonry strips, wherein each masonry strip comprises a plurality of masonry blocks arranged adjacent and horizontally such to occupy a space between two columns of a framed structure,
a sliding element interposed between two adjacent masonry strips, comprising two opposing section bar elements, particularly facing with each other, and intended to longitudinally guide the sliding of a masonry strip with respect to another masonry strip in case of a stress to the infill wall.
a vertical joint element comprising a shear key, intended to be inserted into a seat provided at one end of the infill wall and obtained in a special block of the plurality of blocks, such to allow the shear key to slide in the seat in case of stress to the infill wall.

Claims

Masonry infill wall (6) comprising
- a plurality of superimposed masonry strips (7), wherein each masonry strip (7) comprises a plurality of adjacent masonry blocks (8) horizontally arranged such to occupy a space between two columns (3) of a framed structure (2),

- a sliding element (10) interposed between two adjacent masonry strips (7), characterized in that the sliding element (10) comprises two section bar elements (11) faced with each other and intended to longitudinally guide the sliding of a masonry strip with respect to another masonry strip in case of a stress to the infill wall.
Infill wall according to claim 1, further comprising a vertical joint element (13) comprising a shear key (130) intended to be inserted into a seat (81) provided at one end of the infill wall and obtained in a special block (80) of said plurality of masonry blocks, such to allow the shear key to slide in said seat in case of a stress to the infill wall.
Infill wall according to claim 2, wherein the shear key is obtained by a section bar element, preferably made of steel, to be secured to a column of the structure.
Infill wall according to any of the preceding claims, further comprising a mortar (14) intended to be interposed between the infill wall and one or more elements of the framed structure, said mortar having values of the Young's modulus preferably ranging from 100 to 150 MPa and compressive and flexural strength values higher than 4MPa and 2MPa respectively.
Infill wall according to any of the preceding claims, wherein the section bar elements (11) are made of polymer material and have a corrugated profile in a vertical plane transverse to the development plane of the infill wall.
Infill wall according to claim 5, wherein the polymer material is added or modified with materials reducing the coefficient of friction and facilitate the mutual sliding of the two section bar elements (11).
Infill wall according to any of the claims 1 to 4, wherein at least one of said two section bar elements (11) is as one piece with one or more masonry blocks (8).
Infill wall according to claim 1, further comprising a structural plaster (15) intended to increase the flexural strength of the masonry strips (7) such to allow the masonry strip to withstand an acceleration up to 3g.
Method for making an earthquake-proof infill wall, comprising the steps of:
- providing a plurality of superimposed masonry strips (7), wherein each masonry strip (7) comprises a plurality of adjacent masonry blocks (8) horizontally arranged such to occupy a space between two columns (3) of a framed structure (2),

- interposing between two adjacent masonry strips (7) a sliding element (10), characterized in that the sliding element (10) comprises two section bar elements (11) faced with each other and intended to longitudinally guide the sliding of a masonry strip with respect to another masonry strip in case of a stress to the infill wall.