FIELD OF THE INVENTION

The present invention relates to concrete masonry units for use with elongate reinforcement members in the construction of a masonry wall, and more particularly the present invention relates to concrete masonry units arranged to receive the reinforcement members recessed into the exterior sides of the units.

BACKGROUND

Existing Concrete Masonry Units (CMUs) have two hollow cores and are fabricated with two exterior flat surfaces. When constructing a wall using CMUs they are typically assembled by placing reinforcement and grout in the center of each core. The reinforcement is introduced into the assembly to enable the wall to resist tension stress while the grout is necessary to create a bond between the reinforcement and the concrete blocks. The reinforcement is placed near the centre axis of the block which is also the neutral axis on the wall as a flexural member. When the reinforcement in a flexural member is placed close to the neutral axis it does very little work as the tension stress is zero at the neutral axis. Placing the reinforcement at the centre of the wall also allows the wall to crack at the tension side before the reinforcement begins to work. Cracking of a concrete block wall considerably reduces its durability and increases the operations and maintenance costs while also reducing the design life of the structure. To summarize the issues with the existing system is as follows: i) Tension reinforcement has to be placed at a location where there is little or no tension stress; and ii) In order to create a bond between the reinforcement and the block the core has to be filled with grout increasing material use and self-weight of the structure. This directly increases the cost of the building and carbon footprint of the construction.

SUMMARY OF THE INVENTION

According to one aspect of the invention there is provided a masonry unit arranged for use with elongate reinforcement members in construction of a masonry wall, the masonry unit comprising:

a concrete body which is elongate in a longitudinal direction between two opposing ends of the body, the concrete body further comprising:

a top and a bottom which are arranged for stacking with other masonry units of identical configuration to form the masonry wall;

a first exterior side wall and a second exterior side wall which are parallel and spaced apart from one another to extend in the longitudinal direction between the two opposing ends along opposing sides of the concrete body such that the first and second exterior side walls are arranged to define respective portions of opposing surfaces of the masonry wall; and

at least one hollow core extending through the body between the top and the bottom of the concrete body;

wherein at least one of the exterior side walls includes a reinforcement channel formed therein which extends between the top and the bottom of the body, the reinforcement channel being arranged for vertical alignment with the reinforcement channels of said other masonry units, and the reinforcement channels being arranged for receiving a portion of a respective one of the elongate reinforcement members therein in forming the masonry wall.

According to a second aspect of the present invention there is provided a masonry wall comprising:

a plurality of masonry units as described above which are arranged in stacked rows with mortar between the rows such that the reinforcement channels of at least some of the masonry units are vertically in alignment with the reinforcement channels of other ones of the masonry units;

a plurality of reinforcement members received within respective ones of the reinforcement channels such that the reinforcement members each span across a plurality of the stacked rows at a location recessed laterally inwardly from a respective surface of the masonry wall defined by respective ones of the exterior side walls of the masonry units; and

a bonding material received within the reinforcement channels so as to bond the reinforcement members to the masonry units.

According to a third aspect of the present invention there is provided a method of constructing a masonry wall comprising:

providing a plurality of masonry units as described above and stacking the masonry units in rows with mortar between the rows such that the reinforcement channels of at least some of the masonry units are vertically in alignment with the reinforcement channels of other ones of the masonry units;

providing a plurality of reinforcement members and placing the reinforcement members within respective ones of the reinforcement channels such that the reinforcement members each span across a plurality of the stacked rows at a location recessed laterally inwardly from a respective surface of the masonry wall defined by respective ones of the exterior side walls of the masonry units; and

applying a bonding material to the reinforcement channels so as to bond the reinforcement members to the masonry units.

By providing reinforcement channels in the exterior surfaces of the masonry units, the reinforcement members can be relocated from a central location within the wall towards the surfaces of the wall. The reinforcement channels thus accommodate placement of reinforcement near the extreme tension surface where it is most needed, thereby increasing the loadbearing and flexural capacity of walls constructed using the masonry units, and reducing materials used in constructing the wall. The resulting masonry units are accordingly referred to herein as Surface Reinforced Concrete Masonry Units (SRCMU).

The masonry unit of the present invention is unique in its fabrication as it has vertical channels or grooves on one or both exterior surfaces. The grooves will line up both in running bond and stack bond formation. The continuous groove on the surface of the wall will enable designers and engineers to specify the placement of the reinforcement on the surface of the tension side of the wall. Therefore, the reinforcement is placed near the extreme fiber on the tension side where it is most efficient or "works" the most. Placing the reinforcement on the tension side reduces the tension cracking of the wall therefore increasing the design life of the structure.

The masonry unit of the present invention may be reinforced with Fibre Reinforced Polymer (FRP) rods or specially fabricated glass fibre that can be applied with resin directly or traditional steel reinforcement. FRP reinforcement can be applied with resin containing fire retardant. Traditionally, steel reinforcing has been used in concrete masonry unit construction; however, the masonry unit of the present invention will give the designers the option of using traditional or more efficient reinforcement such as FRP in concrete block masonry construction.

SRCMU can be manufactured using the same fabrication and curing technology as for CMU. The mold has to be modified to accommodate the channels of SRCUM. SRCMU would have the same percentage solid and effective loadbearing area as traditional CMU. Examples of possible dimensions and variations of SRCMU are shown in the accompanying drawings.

The details and the general construction procedure for constructing a wall using SRCMU has also been modified from the traditional concrete block wall system. Grouting the cores are not required since there are no reinforcement in the cores; as noted earlier, grouting facilitates the bond between the reinforcement and the rest of the wall in conventional CMU construction. Elimination of grout will result in many benefits such as reduction of material (rendering the wall assembly and the concrete block wall construction more sustainable), reducing the self-weight of the wall which in turn facilitates the reduction of more construction materials and foundation requirements, and reduces thermal bridging of the wall assembly.

Optionally, neoprene or polystyrene spacers can be placed between two side by side blocks as the wall is being constructed, which means the head joints between each block does not have to be mortared; thereby, reducing material requirement and reducing thermal bridging, while increasing construction speed.

Various embodiments of the invention will now be described in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1A is a top plan view of a first embodiment of the masonry unit with channels on both sides. This unit can be used for the following condition: i) for doubly reinforced wall for additional capacity; ii) when both sides of the wall is exposed and the designers require the same look on both sides; or iii) for when the designers want to have the channels exposed on one side to create a scored look.

Figure 1 B is a sectional view along the line A-A of Figure 1 A.

Figure 1 C is a sectional view along the line B-B of Figure 1A.

Figure 2A is a top plan view of a second embodiment of the masonry unit with channels on one side only. This unit can be used for the following conditions: i) additional capacity of doubly reinforced wall is not required; ii) when the wall is exposed and the designers require a traditional look of concrete block wall; or iii) when used in an addition to an existing structure and the new addition has to match the existing.

Figure 2B is a sectional view along the line A-A of Figure 2A.

Figure 2C is a sectional view along the line B-B of Figure 2A. Figure 3A is a top plan view of a third embodiment of the masonry unit for use as a corner unit in which the unit is exposed at corners of concrete block walls. This unit can also be fabricated one side smooth (without channels) that can be used in the same conditions as indicated for the one side smooth stretcher unit. This unit can also be fabricated as a bullnose block both channel both sides and channel on one side only to accommodate reinforcement.

Figure 3B is a sectional view along the line A-A of Figure 3A. Figure 3C is a sectional view along the line B-B of Figure 3A. Figure 4A is a perspective view of a wall assembly using the masonry blocks units according to Figures 1A to 1C.

Figure 4B is a top plan view of the wall assembly of Figure 4A.

Figure 4C is an enlarged view of the highlighted portion of Figure 4B. Figure 5, Figure 6, and Figure 7 show the relative compressive and moment resistance of various configurations of fully grouted masonry walls.

Figure 8 and Figure 9 show the relative compressive and moment resistance of various configurations of partially grouted masonry walls.

Figure 10 shows the relative compressive and moment resistance of various configurations of ungrouted masonry walls.

Figure 11 and Figure 12 show the strain reaction along the height (z direction) of the SRCMU and CMU masonry prisms, respectively.

Figure 13 and Figure 14 show the strain reaction along the length (x direction) of the SRCMU and CMU masonry prisms, respectively.

Figure 15 and Figure 16 show the strain reaction along the thickness (y- direction) of the SRCMU and CMU masonry prisms, respectively.

Figure 17 shows the maximum stress supported by the prisms constructed from the SRCMUs, LPCMUs, and CCMUs.

Figure 18 shows a test set-up for testing SRCMU units.

Figures 19 and 20 shows the distribution of stresses along the steel reinforcing bars at 50%, 75%, and 100% of the failure load as well as at the point where the steel bar began to yield.

Figures 21 and 22 show the distribution of stresses along the FRP reinforcing bars at 50%, 75%, and 100% of their failure load.

Figure 23 illustrates a test set-up to simulate the behaviour of an SRCMU system under flexural loading conditions.

Figure 24 shows the tensile stresses in the GFRP reinforcing bar on the tension side with little stress being transferred to the reinforcement on the compression side of the prism.

Figure 25 shows the tensile stresses in the steel reinforcing bar on the tension side with little stress being transferred to the reinforcement on the compression side of the prism.

Figures 26 and 27 show the deflection at mid-span and crack width at mid-span, respectively, for a typical steel reinforced specimen and a typical GFRP reinforced specimen.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

Referring to the accompanying figures, there is illustrated a masonry unit generally indicated by reference numeral 10. The masonry unit 10 is particularly suited for use in the construction of a masonry wall 12 as shown in Figures 4A through 4C. The masonry units 10 permit reinforcement members 14, for example conventional rebar or other forms of elongate reinforcement, to be recessed into one or both exterior surfaces of the assembled wall.

The wall 12 is typically constructed in a manner similar to the use of conventional concrete masonry units by abutting the units longitudinally end to end in rows with the rows being stacked one above the other. Each unit may be vertically aligned directly above a corresponding unit in the previous row therebelow, or more preferably each masonry unit 10 is offset longitudinally by half of the length of the unit relative to a corresponding unit of the previous row so that each masonry unit is engaged upon a portion of two additional masonry units therebelow in a conventional brick pattern.

Although various forms of the masonry unit 10 may be provided for various applications, such as at an intermediate location within a wall, at one end of a wall, in a wall reinforced at a single side, or in a wall reinforced on both sides. A common double-sided stretcher unit as shown in Figures 1A through 1C for use at intermediate locations within the wall 12 of Figures 4A through 4C will first be described herein.

Each masonry unit 10 according to Figures 1A through 1C comprises a concrete body such that the body is seamless, unitary and integral as a single body. The body is generally rectangular in shape including a flat top 20 and a flat bottom 22 so as to be suitably arranged for vertical stacking in the masonry wall construction.

Each body is also elongate in a longitudinal direction between two opposing ends 24.

A first exterior side wall 26 and a second exterior side wall 28 extend longitudinally along laterally opposed sides of the body between the two opposing ends while spanning the full height between the top and bottom of the body. The exterior side walls define respective portions of the two opposing surfaces of the finished wall 12.

The body includes two hollow cores 30 formed therein at longitudinally spaced positions to extend fully through the body between the top and bottom thereof. The two hollow cores 30 are separated longitudinally by a web portion 32 which is connected between the first and second exterior side walls at a longitudinally centered location. The web portion thus extends in a lateral direction between the two opposing side walls. The web portion spans the full height between the top and bottom of the body.

Two end walls 34 are provided for enclosing the two opposing ends of the body such that one of the hollow cores is defined between the web portion 32 and each one of the two end walls 34.

Inner surfaces of the web portion, the end walls, and the exterior side walls may be formed with a slight inclination from vertical to aid in releasing the concrete body from a respective concrete mold.

The body of each masonry unit further includes a reinforcement channel 36 formed in each one of the two exterior side walls. Each reinforcement channel is longitudinally centered between the opposing ends of the body and spans the full height between the top and bottom sides of the body. Each channel is a generally U- shaped and is opened to the exterior of the body.

By being longitudinally centered, each reinforcement channel aligns laterally with the web portion 32. The web portion increases in thickness as measured in the longitudinal direction of the block from the center, laterally outward towards each of the two exterior side walls locating the reinforcement channels 36 therein to provide additional reinforcement of material about each channel.

Each end of the block further includes a partial channel 38 along the exterior sidewall at the end of the body. The partial channel is located at the intersection of the end wall and the exterior side wall so as to be open to both the end and the exterior side of the block. The partial channel 38 spans the full height between the top and bottom. The shape and depth of the partial channel 38 is arranged such that when two masonry units of identical configuration are abutted end to end using mortar (or a spacer element described further below) between the units, the resulting combination of two adjacent partial channels 38 defines a whole reinforcement channel of identical configuration to the reinforcement channels 36 at the intermediate location along each exterior side wall. Each of the reinforcement channels, including integral channels 36 or channels formed by the abutment of two partial channels 38, is vertically aligned with corresponding reinforcement channels of masonry units stacked above and below the respective unit to form respective portions of a vertical recess spanning the height of the assembled masonry wall. In this manner, the reinforcement channels are arranged to receive the reinforcement members 14 therein such that the members span across several rows within the channels so as to be recessed inwardly relative to the resulting exterior face of the assembled masonry wall. The reinforcement channels 36 are accordingly suitably sized to receive the reinforcement members therein as well as additional bonding material 40 to bond the reinforcement members to the masonry units across several rows of units.

Each of the end walls 34 is further shaped to define a recessed channel 42 at a central location in the lateral direction such that the channel 42 spans the full height of the unit between the top and bottom thereof. The recessed channel 42 is recessed longitudinally inward relative to adjacent portions of the end face 44 defined by the end wall. Each end face 44 spans the full height and spans in the lateral direction from the recessed channel towards the respective exterior side wall of the body. When partial channels 38 are provided the end faces 44 span between the recessed channel and a respective one of the partial channels 38 at the end of the body.

In the illustrated embodiment, the masonry units 10 are used in combination with spacer members 46 in which each spacer member is abutted between the two ends of two adjacent masonry units within a respective row of the masonry wall. The spacer member comprises a body of rigid insulation having a profile which mates with the corresponding exterior profile of the end wall 34 of the body of the masonry unit 10.

More specifically, each spacer member comprises two side portions 48 and a central portion 50 located between the two side portions in the lateral direction such that all three portions span the full height of a single masonry unit. The central portion 50 is suitably sized to be received within the recessed channels 42 of two adjacent masonry units abutted on either side of the spacer member. The two side portions are reduced in thickness in the longitudinal direction of the masonry units so as to be suitable for abutment with the corresponding end faces 44 on either side of the recessed channels 42.

The overall width of the spacer member in the lateral direction between opposing exterior sides of the masonry units is arranged to be less than the body of the masonry units such that the opposing ends of each spacer member are recessed inwardly relative to the exterior surface of the exterior side walls in the finished masonry wall construction. More particularly the spacer member terminates at opposing ends adjacent the innermost portion of the partial channels 38 such that the spacer member does not protrude into or obstruct the resultant reinforcement channel 36 formed by the abutment of two partial channels 38. In this manner, the reinforcement channel assembled from two partial channels remains unobstructed to allow the respective portion of the reinforcement member to be received therein while also permitting the spacer body to be hidden within the wall when covered by the reinforcement member and/or corresponding mortar or other finishing bonding material at the exterior or the masonry wall.

Construction of a masonry wall using the unit 10 typically involves initially applying a layer of levelling grout upon which a first row of masonry units are positioned in a longitudinally end-to-end abutted relationship with spacer members 46 or mortar being received between each adjacent pair of masonry units. Each subsequent row of masonry units is stacked on the previous row by first applying a layer of mortar across the tops of the masonry units of the previous row followed by another row of longitudinally aligned end-to-end abutted masonry units.

In the preferred arrangement, each masonry unit is offset by half the length of a unit relative to corresponding units of the previous row such that each reinforcement channel 36 is vertically aligned with a corresponding reinforcement channel formed by two partial channels 38 in the previous row therebelow. Likewise each reinforcement channel formed by the abutment of two partial channels in the current row is vertically aligned directly above a corresponding integral reinforcement channel of the previous row therebelow. The hollow cores are similarly vertically aligned with the hollow cores of units of the previous rows.

Subsequent to the stacking of the masonry units in the form of the masonry wall, the reinforcement members are recessed into one or both exterior faces of the masonry wall by being received within respective reinforcement channels with each reinforcement member spanning across multiple rows of units. The reinforcement members are retained within the respective reinforcement channels using the bonding material 40, which is also recessed into the channels relative to the exterior surface of the assembled wall structure. In this manner, the bonding material covers the reinforcement members within the interior of the assembled wall structure as well as covering any spacer members 46 which were used in abutment between adjacent masonry units.

The reinforcement members may take various forms including steel rods, glass fiber rods, fiber reinforced polymer rods or any other suitable elongate member having sufficient tensile strength to reinforce the assembled masonry wall structure.

Similarly, the bonding material may take various forms. For example, the bonding material may comprise mortar, epoxy, or other curable resins and the like.

The reinforcement members may be provided in all reinforcement channels at one or both sides of the assembled wall, or alternatively only at selected channels longitudinally spaced apart as required to meet strength requirements.

The masonry unit described above with regard to Figures 1A through 1C is particularly suited for use at an intermediate location within a wall where the option of reinforcement at both sides of the wall is desired.

Alternatively, if it is clear the reinforcement is only required at one of the two surfaces of the masonry wail, a single-sided masonry unit as shown in Figures 2A through 2C may be provided. The masonry unit 10 shown in Figures 2A through 2C is identical to the first embodiment with the exception of one of the first or second exterior sides comprising a flat side 70 spanning the full length of the body in the longitudinal direction so as to be uninterrupted by any reinforcement channels, either whole or partial.

In yet a further consideration, where it is desired for the finished masonry wall to terminate at a free end, a bullnose masonry unit may be provided as shown in Figures 3A through 3C. The masonry unit 10 shown in Figures 3A through 3C is identical to the first embodiment with the exception of one of the two opposing ends comprising a flat surface 80 spanning the full height and width of the end of the body so as to be free of any recessed channel or partial channels described above.

In this instance, a plurality of half blocks 90 are also typically provided, as shown in Figure 4A, which are half the length of a typical masonry unit so that all of the rows terminate at a common location even when the blocks are offset by half a length relative to adjacent rows in a conventional brick pattern.

Relationship between Compressive Resistance and Moment Resistance

The following sections illustrate the potential strength of walls constructed of surface reinforced masonry units compared to those made from conventional hollow masonry units. Figures 5 to 10 show the Compressive resistance vs. Moment resistance diagrams (Pr-Mr diagrams) for walls with the same thickness and reinforcement ratio. The curves seen in Figures 5 to 10 were developed using the methodology described in CSA S304.1-04 as prescribed by the National Building Code of Canada. The model used to determine the stress in the masonry units and grout was the equivalent rectangular stress block (S304.1 -04 10.2.6). Table 1 shows the variables used for the application of CSA S304.1-04 for the purposes of this document. It was assumed that the surface reinforced units would behave in the same way as conventional hollow masonry units, the only difference being the location of the reinforcing steel.

Table 1

Variable Value Value justification

A _e (effective cross sectional area of varies Varies according to the masonry per 1 m length of wall) percentage of cores that are grouted

As (total cross sectional area of steel 300 mm ² Dictated by the reinforcement rebar per 1 m length of wall) ratio (p)

Ast (cross sectional area of steel rebar 150 mm ² Dictated by the reinforcement near the tension face of the wall per 1 m ratio (p)

length of wall)

Asc (cross sectional area of steel rebar 150 mm ² Dictated by the reinforcement near the compression face of the wall ratio (p)

per 1 m length of wall)

b (effective width of the test wall 1000 mm Typically used for analysis section)

bw (effective width of the grouted cores 400 mm Consistent with 2 grouted in partially grouted walls per width b) cores per meter width of wall c (depth from the compression face of varies Varies from 0 to infinity in the wall to the neutral axis) order to construct the P _r -Mr

diagrams

Cm (compression force from masonry varies Varies depending on the rectangular stress block) design and the depth to neutral axis (c)

Cmfi (compression force from masonry varies Varies depending on the rectangular stress block in the face shell design and the depth to near the compressive face of the wall) neutral axis (c)

Cmf2 (compression force from masonry varies Varies depending on the rectangular stress block in the face shell design and the depth to near the tension face of the wall) neutral axis (c)

Cmw (compression force from masonry varies Varies depending on the rectangular stress block in the grouted design and the depth to cores of the wall) neutral axis (c)

Cs (force in the stee! rebar near the varies Varies depending on the compression face of the wall) design and the depth to neutral axis (c)

d (depth to reinforcing steel for 95 mm Centre of masonry unit conventional units)

di (depth to reinforcing steel on the 10 mm Varies depending on design compression face of the surface

reinforced units)

d2 (depth to reinforcing steel on the 180 mm Varies depending on design tension face of the surface reinforced

units)

Es (Modulus of elasticity of steel rebar) 200,000 S304.1-04 6.5.1

MPa

f'm (masonry compressive strength) 10 MPa Typical value for general use masonry

f _y (yield strength of steel rebar) 400 MPa S304.1 -04 10.2.3

fst (stress in steel rebar at centre line or varies Varies according to the strain near the tension face of the wall) in the steel ( st)

fsc (stress in steel rebar near the varies Varies according to the strain compression face of the wall) in the steel (e _S c)

Mr (moment resistance of a masonry varies Varies depending on the wall, per width b) design and the depth to neutral axis (c)

Pr (compressive resistance of a varies Varies depending on the masonry wall, per width b) design and the depth to neutral axis (c)

t (wall thickness) 190 mm Typical block type for general use

T (force in the steel rebar in the varies Varies depending on the centreline of the wall or near the tension design and the depth to face) neutral axis (c) tf (thickness of the masonry unit face 32 mm Typical (Hatzinikolas 2005) shell)

βι (ratio of depth of rectangular 0.8 S304.1-04 10.2.6

compression block to depth of neutral

axis)

£m (maximum usable masonry strain) 0.003 S304.1 -04 10.2.2

Est (strain in steel rebar at centreline or varies Varies depending on the near the tension face of the wall) design and the depth to neutral axis (c)

£sc (strain in steel rebar near the varies Varies depending on the compression face of the wall) design and the depth to neutral axis (c)

p (reinforcement ratio) 0.158 % Arbitrary amount allowed by

S304.1-04

<jte (steel rebar resistance factor) 0.85 S304.1-044.3.2.2

<j)m (masonry resistance factor) 0.6 S304.1 -044.3.2.1

χ (factor used to account for direction of 1.0 For out of plane vertical compressive stress in a masonry bending S304.1 -04 10.2.6 member relative to the direction used for

the determination of f'm)

Table 2 explains the shorthand used to identify the various configurations of masonry walls analysed for the purposes of this section of the text.

Table 2

SR Surface reinforced masonry units

C Conventional masonry units

UT Steel reinforcement not tied

T Steel reinforcement tied UR Un reinforced (no steel reinforcement)

G Fully grouted cores

PG Partially grouted cores

UG Ungrouted (no cores grouted)

Example: SR/UT/G means the wall is composed of surface reinforced masonry units (SR) reinforced with steel rebar that is not tied (UT) and fully grouted (G).

First will be discussed configurations in which all the cores in the wall are filled with grout (SR/UT/G, C/UT/G, SR/T/G, C T/G and C/UR/G). For the cases where the reinforcing steel is not tied and when no reinforcing steel is used, the maximum factored compressive resistance (Pr(max)) is calculated as:

Pr(max>=0.80 (0.85<pmfmA _e ) S304.1-04 10.4.1/7.4

For the cases where the reinforcing steel is tied, Pr(max) is calculated as:

Pr(max)=0.80 (0.85<pmf'm(Ae-As)+CpsfyA _s ) S304.1 -04 10.4.2

Factored compressive resistance (Pr) and moment resistance (Mr) must satisfy conditions of equilibrium and compatibility of strain (S304.1 -04 10.1.1). For grouted CMU walls to satisfy conditions of equilibrium of forces, the following equation must be satisfied:

Pr=Cm-T

Where:

is the compressive force in the masonry (S304.1 -04

10.2.6).

and

is the tension force in the steel rebar. Where is the tension stress in the steel rebar and As is the cross-sectional area of the steel rebar {S304.1-04 10.2.3).

For grouted CMU walls to satisfy conditions of equilibrium of moments the following equation must be satisfied:

For grouted CMU walls to satisfy conditions of compatibility of strain the following equation must be satisfied:

For grouted SRCMU walls to satisfy conditions of equilibrium of forces the following equation must be satisfied:

Pr ⁼ Cm+Cs"T

Where:

is the compressive force in the masonry (S304.1 -04

10.2.6).

Cs=q>sfscAsc is the compressive force in the steel rebar. Where is the compressive stress in the steel rebar and Asc is the cross- sectional area of the steel rebar near the compression face (S304.1 -04 10.2.3).

and

is the tension force in the steel rebar. Where is the tension stress in the steel rebar and Ast is the cross-sectional area of the steel rebar near the tension face (S304.1-04 10.2.3).

For grouted SRCMU walls to satisfy conditions of equilibrium of moments the following equation must be satisfied:

For grouted SRCMU walls to satisfy conditions of compatibility of strain the following equation must be satisfied:

Figure 5, Figure 6, and Figure 7 show the relative compressive and moment resistance of various configurations of fully grouted masonry walls. The maximum compressive resistance of the wall made from surface reinforced masonry units is no greater than that of conventional masonry units, however the moment resistance of the wall is greatly improved by the use of surface reinforced units. This can be seen by comparing SR/T/G to C7T/G and SR/UT/G to C/UT/G. As expected, the unreinforced wall has the lowest moment resistance and shows the same behaviour for both types of masonry.

Considering partially grouted configurations in which only a portion of the cores in the wall are filled with grout (SR/UT/PG, C/UT/PG, SR T/PG and C/T/PG), for the cases where the reinforcing steel is not tied and when no reinforcing steel is used, Pr(max) is calculated as:

Pr(max)=0.80 (0.85<pmf'mA _e ) S304.1-04 10.4.1/7.4

For the cases where the reinforcing steel is tied, Pr(max) is calculated as: (0.85φΓϊ ₁ ί' _Γ η(Αβ-Α8)+φ8ί _γ Α3) S304.1-04 10.4.2

Factored compressive resistance (Pr) and moment resistance (Mr) must satisfy conditions of equilibrium and compatibility of strain (S304.1 -04 10.1.1 ). For partially grouted CMU walls to satisfy conditions of equilibrium of forces, the following equation must be satisfied:

Pr=Cmf1 +Cmw+Cmf2-T

Where:

; (pm0.85f'mxbtf} is the compressive force in the face shell near the compressive face of the wall (S304.1 -04 10.2.6).

; max {0 ; cpm0.85fmxb(pic-tf)}} is the compressive force in the grouted cores of the wall (S304.1 -04 10.2.6).

Cmf2=max{0 ; (pm0.85fmxb( ic-t+tf)} is the compressive force in the face shell near the tension face of the wall (S304.1-04 10.2.6).

is the tension stress in the steel rebar and As is the cross-sectional area of the steel rebar (S304.1-04 10.2.3).

For partially grouted CMU walls to satisfy conditions of equilibrium of moments the following equation must be satisfied:

; t _f /2})+Cmw*(max{t/2-(pic-tf)/2 ; 0})+Cmf2 ^* $ic-tf/2 )+C _s ^* (t/2-di)- T ^* (t 2-d ₂ )

For partially grouted CMU wall to satisfy conditions of compatibility of strain the following equation must be satisfied:

For partially grouted SRCMU walls to satisfy conditions of equilibrium of forces the following equation must be satisfied:

Pr=Cmf1+Cmw+Cmf2+Cs-T Where:

; (p _m 0.85f'mxbtf} is the compressive force in the face shell near the compressive face of the wall (S304.1 -04 10.2.6).

; max {0 ; q> _m 0.85fmxb$ic-tf)}} is the compressive force in the grouted cores of the wall (S304.1-04 10.2.6).

Cmf2=max{0 ; <pm0.85fmxb(Pic-t+tf)} is the compressive force in the face shell near the tension face of the wall (S304.1-04 10.2.6).

Cs=cpsfscAsC is the compressive force in the steel rebar. Where fsc=min{£scE _s ;fy} is the compressive stress in the steel rebar and Asc is the cross- sectional area of the steel rebar near the compression face (S304.1 -04 10.2.3).

is the tension stress in the steel rebar and Ast is the cross-sectional area of the steel rebar near the tension face (S304.1-04 10.2.3).

For partially grouted SRC U walls to satisfy conditions of equilibrium of moments:

; tf/2})+Cmw*(max{V2-( c-tf)/2 ; 0})+Cmf2 ^* (( ic-tf)/2 )+C _s *(t 2- d1)-T ^* (t/2-d2)

For partially grouted SRCMU walls to satisfy conditions of compatibility of strain:

Figure 8 and Figure 9 show the relative compressive and moment resistance of various configurations of partially grouted masonry walls. Similar to the fully grouted walls, the maximum compression resistance of the wall does not change with the type of masonry unit (conventional or surface reinforced). By comparing SR T/PG to C/T/PG and SR/UT/PG to C/UT/PG, once again an appreciable gain in moment resistance can be observed for the surface reinforced masonry walls as compared to the conventional masonry walls.

Considering ungrouted configurations in which none of the cores in the wall are filled with grout (SR/UT/UG, SR/T/UG and C/UR/UG), for the cases where the reinforcing steel is not tied and when no reinforcing steel is used, Pr(max) is calculated as:

(0.85cp _m f'mAe) S304.1 -04 10.4.1/7.4

For the cases where the reinforcing steel is tied, Pr(ma ) is calculated as: (0.85(pmf'm(Ae-As)+q>sfyAs) S304.1 -04 10.4.2 Factored compressive resistance (Pr) and moment resistance (Mr) must satisfy conditions of equilibrium and compatibility of strain (S304.1-04 10.1.1). For ungrouted CMU walls to satisfy conditions of equilibrium of forces, the following equation must be satisfied:

Where:

; cpm0.85f'mxbtf} is the compressive force in the face shell near the compressive face of the wall (S304.1-04 10.2.6).

Cmf2=max{0 ; <pm0.85f'mxb(pic-t+tf)} is the compressive force in the face shell near the tension face of the wall (S304.1-04 0.2.6).

For ungrouted CMU walls to satisfy conditions of equilibrium of moments the following equation must be satisfied:

; tf/2})+Cmf ₂ *((Pic-t _f )/2)

There is no need to check compatibility of strain for C/UR/UG since there is only one material. For ungrouted SRCMU walls to satisfy conditions of equilibrium of forces the following equation must be satisfied:

Where:

; cpm0.85fmxbtf} is the compressive force in the face shell near the compressive face of the wall (S304.1-04 10.2.6).

Cmf2=max{0 ; <pm0.85f'mXb(Pic-t+tf)} is the compressive force in the face shell near the tension face of the wall (S304.1-04 10.2.6).

Cs=cp _s fscAsc is the compressive force in the steel rebar. Where is the compressive stress in the steel rebar and Asc is the cross- sectional area of the steel rebar near the compression face (S304.1-04 10.2.3).

is the tension force in the steel rebar. Where is the tension stress in the steel rebar and A _s t is the cross-sectional area of the steei rebar near the tension face (S304.1 -04 10.2.3).

For ungrouted SRCMU walls to satisfy conditions of equilibrium of moments the following equation must be satisfied:

; tf/2})+Cmf2*(( iC-tf)/2)+Cs ^* (t 2-di)-r(t 2-d ₂ )

For ungrouted SRCMU walls to satisfy conditions of compatibility of strain the following equation must be satisfied:

Figure 10 shows the relative compressive and moment resistance of various configurations of ungrouted masonry walls. In conventional masonry construction, grout is used to bond the reinforcing steel bars to the masonry assemblage, conventional masonry practices therefore do not allow ungrouted masonry walls to be vertically reinforced. Using surface reinforced masonry units it is possible to vertically reinforce ungrouted masonry walls, greatly increasing the wall's moment resistance without the added weight of grout.

Distribution of Strain Under Axial Loading

It is common practice to test the strength of masonry units by testing prisms made from two masonry units stacked one on top of the other with a single mortar bed between them. The figures 11 to 16 illustrate the strain reaction of conventional hollow masonry units as well as surface reinforced units. Since the purpose is to verify the behaviour of the unit itself, both prisms are left ungrouted and unreinforced. The ANSYS Mechanical finite element modeling package was used to model the prisms because of its versatility and because it is commonly used in industry.

A linear elastic material model was used to represent both the masonry unit and the mortar. The material properties of the masonry units and mortar bed are shown in Table 3. Typical values were obtained from Drysdale (2005). The effect of self-weight of the units and mortar was neglected.

Table 3 Masonry unit Mortar

Young's 8500 MPa Young's 4250 MPa

modulus modulus

Poisson ratio 0.2 Poisson ratio 0.18

Specifications of the numerical model are shown in Table 4. Both prism models were subjected to an axial pressure of 10MPa with the prisms confined at the top and bottom surfaces (typical of laboratory conditions).

Table 4

Figure 1 and Figure 12 show the strain reaction along the height (z direction) of the SRCMU and CMU masonry prisms, respectively. As expected, the more flexible mortar joint reacts with much higher strain levels than the masonry units. Both types of masonry unit react with very similar patterns of strain.

Figure 13 and Figure 14 show the strain reaction along the length (x direction) of the SRCMU and CMU masonry prisms, respectively. Here some differences exist between the two types of masonry units. Tension strain is higher in the middle section of the surface reinforced unit (near the centre web) because of the reduced cross section as compared to the conventional unit. However, both types of units exhibit higher strains near the cored sections of the unit than near the centre web.

Figure 15 and Figure 16 show the strain reaction along the thickness (y- direction) of the SRCMU and CMU masonry prisms, respectively. Here the geometry of the surface reinforced unit appears to relieve some of the strain near the centre web of the unit. No additional strain concentrations appear to exist in the surface reinforced prism when compared to the conventional prism.

Physical Testing Axial Compressive Behaviour

Testing of physical specimens were conducted to compare the behaviour of stack bonded masonry prisms constructed of conventionally shaped hollow concrete masonry blocks to those constructed of SRCMUs under axial compressive stresses. 5 masonry prisms were constructed using SRCMUs produced in laboratory, 3 prisms were constructed of conventionally shaped masonry blocks produced in laboratory (LPCMU), and 3 prisms were constructed from commercially available conventional hollow concrete blocks (CCMU). All specimens (four blocks high each) were constructed on the same day by a skilled mason.

To ensure that they had reached their maximum load-carrying capacity, all eleven specimens were tested to failure, more than 28 days after they had been produced.

Figure 17 shows the maximum stress supported by the prisms constructed from the SRCMUs, LPCMUs, and CCMUs. The average strength for the three different populations of prisms varied by less than 22% from the global average, and the coefficient of variation of the entire population of masonry prisms at, 9.7%, is well within the 15% limit set by Annex D of S304.1 for small samples of prisms. The coefficient of variation of elastic modulus measured for the prisms was 8.1 %. Together, these results suggest both that the blocks manufactured in the laboratory have similar compressive properties to those that were commercially produced and that blocks with the SRCMU cross-section have similar compressive properties to those that have the conventional hollow block cross-section.

An analysis of the modes of failure observed during the compression testing of masonry prisms has yielded three different modes of failure; vertical splitting of the web, vertical splitting of the face shell, and diagonal splitting of the face shell. These three modes of failure were observed to some extent in all eleven masonry specimens tested.

Neither the analysis of the strength of the masonry prisms nor their modes of failure suggest that a significant difference in compressive behaviour exists between conventional hollow masonry blocks and SRCMUs.

Physical Testing Development of Reinforcement Stresses

In order for a reinforcing bar to allow a masonry system to develop its required flexural strength, the reinforcing bars must be properly anchored. In order for a reinforcing system to be practicable, adequate anchorage of reinforcing bars must be achievable within a short distance.

A pull out test was devised in order to determine the bond characteristics as well as the modes of failure of SRCMU systems reinforced with steel rebar or with Fibre Reinforced Polymer (FRP) reinforcing bars. For this test, reinforcing bars were mechanically pulled out from three-high stack-bonded SRCMU prisms into which they had been installed using epoxy grout. The reinforcing bars were fitted with instrumentation to determine the distribution of forces within the bars as they were being pulled out

Six specimens were constructed for this test; 3 specimens were reinforced using 10M steel rebar, and 3 specimens were constructed using 9.5mm FRP reinforcing bars. Each reinforcing bar was fitted with six strain gauges at intervals of 100mm in order to accurately quantify the distribution of forces within the bars during loading.

The full test set-up is shown in figure 18. The masonry specimen (101) is restrained against the loading platens (102) with four steel angles (103) and four threaded rods (104). A sheet of fibre board (105) and a steel plate (106) are used to distribute the loads from the restraining device to avoid stress concentrations in the blocks which would cause premature failure. The free end of the reinforcing bar (107) is anchored into the restraining block (108) of the testing frame.

Figures 19 and 20 shows the distribution of stresses along the steel reinforcing bars at 50%, 75%, and 00% of the failure load as well as at the point where the steel bars began to yield. Figures 21 and 22 show the distribution of stresses along the FRP reinforcing bars at 50%, 75%, and 100% of their failure load. Note that figures 19 and 21 show specimens for which the mode of failure was the rupture of the bar and figures 20 and 22 show specimens for which the mode of failure was the pulling out of the bar from the channel. Given the similarities in behaviour apparent in figures 19 and 20 and figures 21 and 22, it appears that both 10M steel bars and 9.5mm GFRP bars are near the limit of strength which may be developed by the SRCMU system used for this experimental programme. Further examination of Figures 19 to 22 indicate that there was a high likelihood for progressive debonding of the bars to occur for all specimens, since high stress levels in the bars could be observed in the lower portion of specimens. This theory is supported by the observation that 50% of the specimens tested failed by progressive debonding of the reinforcing bar before the bar ruptured.

The lower force at which the GFRP bars pulled out of the masonry specimens is due to the lower modulus of elasticity (higher flexibility) of the material, which causes stresses to concentrate more near the free end of the bar on which the force is applied; this causes the bond between the bar and the concrete to fail progressively away from the applied force.

Also of note is that the yield stress (value used for engineering design) of the steel bars was achieved with no significant damage to the specimens. It can therefore be said that the yield strength of the 10M steel bar was developed within 600mm (the height of the pull-out specimens). This compares well with the length required to develop the strength of steel rebar with masonry grout from CSA S304.1 , which for a common grout strength of f' _g r=10MPa and no modification factors would be.

Id= 0.45*ki k2k ₃ (f _y /fgr- ² )db l _d =0.45 ^* 1 ^* 1 ^* 1 ^* (400MPa/(10MPa) ^"2 )1 Omm

Physical Testing. Flexural Behaviour

To simulate the behaviour of an SRCMU system under flexural loading conditions, six specimens were constructed to be tested in four-point loading conditions. The configuration of the specimens is illustrated in figure 23; each specimen is constructed of six SRCMUs (101 ) bonded vertically, and reinforced in compression and tension with reinforcing bars (102). The specimens are supported at points (103) and loaded at points (104). Strain gauges are located at points (105) along the length of each reinforcing bar in order to determine the stress at those locations. Other data collected includes crack width and deflection at mid-span of the prism.

Using the approach from CSA S304.1 and removing the material factors, the failure load of the specimens can be estimated:

Assumptions:

• Equilibrium of forces Cr=Tr

• Sufficient development length is provided to develop the full tensile strength for the reinforcing materials.

For steel reinforced specimens:

Tension resistance:

Tr=Asf _y

Compression resistance:

Symbol Value Source

f'm Masonry compressive strength=20MPa Compression testing

fy Steel yield strength=400 Pa Material data sheet

fs Stress in compression steel=variable -

As Steel reinforcement cross sectional Material data sheet

area=100mm ² A's Compression steel reinforcement cross- Material data sheet sectional area=100mm ²

b Width of rectangular stress Measured

block=180mm

a Depth of rectangular stress

block=variable

Mr Moment resistance of the prism=variable - d Distance from top of prism to tension Measured

reinforcements 70mm

Cr=Tr

f'm0.85ab+fsA's=Asfy

a=14.7mm

Mr=6.5kNm

Total load = 2 ^* Mr/0.33m

Total load = 39.4 kN

For FRP reinforced specimens:

Tension resistance:

Tr=Afrpfr

Compression resistance:

Symbol Value Source

f'm Masonry compressive strength=20MPa Compression testing fr FRP rupture strength=1100MPa Material data sheet fs FRP compression stress=variable -

Afrp FRP reinforcement cross sectional Material data sheet area=71.3mm ² A'frp Compression FRP reinforcement cross Material data sheet

sectional area=7l .3mm ²

b Width of rectangular stress block=180mm Measured

a Depth of rectangular stress

block=variable

Mr Moment resistance of the prism=variable - d Distance from top of prism to tension Mesaured

reinforcements 70mm

Cr=T _r

f'm0.85ab-f-fsA'frp=Tr

a=24.4mm

Mr=12.3kNm

Total load = 2 ^* Mr/0.33m

Total load = 75.0 kN The high flexural resistance of the specimens being tested resulted in all

6 specimens failing in diagonal tension (also known as shear). However, the observed strength of the specimens nonetheless compare well with anticipated results. Figure 24 shows the increase in tensile stresses in the GFRP reinforcing bar on the tension side (strain gauges 201 to 203) with little stress being transferred to the reinforcement on the compression side of the prism (strain gauge 204). The higher tension stress in strain gauge 202 compared to gauges 201 and 203 is due to its location within the central mortar joint of the specimen; this location is most likely to crack, forcing the reinforcing bar to withstand the entire tensile stress at that location.

A similar behaviour can be observed in the steel reinforced specimens as shown in Figure 25. The main difference in behaviour between the steel reinforced specimens and the GFRP reinforced specimens is the higher stiffness of the steel reinforcing bars, which causes much lower strain values under similar stress conditions.

Figures 26 and 27 show the deflection at mid-span and crack width at mid-span, respectively, for a typical steel reinforced specimen and a typical GFRP reinforced specimen. As expected, deflections and crack width are significantly lower for the steel reinforced specimens compared with the GFRP specimens. However, all specimens exhibited roughly linear behaviour up to approximately 50% of their strength, followed by an increased rate of deflection until total failure occurred. This type of behaviour is beneficial in engineering design as it allows for conspicuous signs of deterioration in a building system before total failure occurs.

The following references referred to in the above description are incorporated herein by reference.

CSA (2004) CSA S304.1 -04 (R2010) Design of Masonry Structures, Canadian Standards Association, Mississauga, Ontario

Drysdale RG, Hamid AA (2005) Masonry Structures Behaviour and Design Canadian Edition. Canadian Masonry Design Centre, Mississauga, Ontario

Hatzinikolas MA, Korany Y (2005) Masonry Design for Engineers and Architects. Canadian Masonry Publications, Edmonton, Alberta

Since various modifications can be made in my invention as herein above described, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.