The Shearline module in MASS is a useful tool to quickly and easily determine how lateral, in-plane forces are distributed within a single elevation. While the scope of the shearline module is relatively basic and relies upon a number of simplifying assumptions in the analysis, it doesn’t take much time to gain an understanding of how these loads are distributed around openings and movement joints.

One of the required steps before the loads are distributed is for the user to review the position and geometry of each pier and decide whether it be modeled as “Fixed” or “Cantilever”. More specifically, as an elevation is laterally loaded, whether each element’s deflection would more closely resemble that of a fixed or cantilever shear wall. Below is an illustration of how a shear wall deflects when the top end fixity is left unrestrained, or cantilever (top), compared to a shear wall deflecting with the top end condition fixed, restricting only rotation (bottom).

While the difference has a big effect on the design of the shear wall (fixed top reduces factored moment by 50%, two critical sections instead of one), the important aspect when modelling a shearline is lateral stiffness and rigidity. Cantilever shear walls deflect more than those that are fixed from rotating therefore attracting less load relative to the other shear walls within the elevation. An example I posted online a few years ago is included below and runs through the entire process of designing a shear wall elevation using the Shearline module in MASS.

Looking at the example from the video, consider the two piers highlighted below:

The leftmost pier has nothing above it to restrict lateral rotation so it’s behaviour would more closely resemble that of a cantilever pier. Conversely, the pier on the right has a significant area of masonry which would more likely cause it’s deflected shape to more closely resemble that of a fixed pier.

How to decide of a pier is modeled as a Fixed or Cantilever shear wall

When MASS Version 2.0 was in development, CMDC looked into creating an algorithm that could look at an elevation and automatically designate each element as fixed or cantilever. Unfortunately, development of this functionality did not proceed very far because there was nothing in any building codes, CSA standards, or even consensus within the design community regarding what exactly constitutes fixity at the top of a shear wall. As a result, end fixities were left as direct user inputs, having to be manually assigned by the designer, using their professional engineering judgement, each time a Shearline is created.

Often when there is a difficult engineering judgement, the response it to make the more conservative decision. While there are other design decisions in the development of MASS where choices were made in the interest of remaining conservative, there is no clear-cut “conservative” decision when it comes to lateral load distribution. While a fixed shear wall deflects less (thus attracting a larger shear force due to the increased rigidity) compared to a cantilever shear wall, it is important to remember that lateral, in-plane load distribution is relative. What increases loading for one element will take away from all of the others.

It is no coincidence that the examples shown on the MASS website, in the help files (found by pressing F1 within MASS), in the CMDC Masonry Design Textbook, or shown here highlight cases that are not particularly controversial when it comes to differentiating between fixed and cantilever behaviour. As an example, consider Figure 40 (shown below) from section 6.2 of the MASS Help Files demonstrating a) highlighted piers that would behave as cantilever compared to b) highlighted piers that would behave as fixed shear walls:

The reality is that there are many cases in the middle that can be taken either way with arguments on both sides having valid and rational points. At the end of the day, it is left up to the judgement of the engineer to make the final call.

If you have any questions, please do not hesitate to call or email the Canada Masonry Design Centre.

The MASS software is a product of a joint partnership between CMDC and CCMPA. CMDC is the authorized provider for MASS Technical Support.

The MASS software is a useful tool for designing the individual structural elements of a masonry building. While there is a shearline module for simple, single-storey elevations, there is no such equivalent when it comes to multi-storey shear wall design (yet). It is left to the designer to model each element of their shear wall within MASS in a way that accurately represents its behaviour. This article will touch on a few of the major aspects that come up when using MASS for multi-storey designs.

To jump straight to a specific aspect, click the heading links below:

• Load Distribution
• Total Height
• Top End Fixity

Click here to jump straight to the summary. 

Load Distribution

Before diving into the multi-storey specifics of shear wall design, it is useful to first recall the scope of the shear wall module in MASS.

Shear wall module scope:

The shear wall module in MASS designs an individual shear wall element for in-plane moment and shear based on the loads that are applied to that individual element.

The shear wall module can be used for multi-storey buildings so long as the designer has taken into account the various ways in which a shear wall element interacts with the structure around it.

This includes:

• The accumulation of axial loads applied above the storey being designed
• The accumulation of lateral loads applied above the storey being designed
• Any overturning moments resulting from lateral loads applied above the top of the storey being designed

Example Exercise

Consider the example below, where the second storey of a four storey shear wall is being designed using MASS. In order to design the second floor shear wall element, all loads must be distributed to the top of the wall from all of the walls above. Each storey is 4m tall and all dead loads include self-weight.

Before expanding the solution, it may be a worthwhile exercise to calculate the solution yourself to test your skills.

Note: All axial loads are assumed to be placed at the centre of the wall and evenly resisted by the full cross section (no load dispersion is considered within the section). In cases where axial loads are applied with some eccentricity, this can be accounted for in MASS using an applied moment with a moment arm equal to the eccentricity of the load.

While distributing loads makes up the majority of the work needed to design multi-storey shear walls in MASS, there are still three other important aspects to consider.

Total Height

It is possible that while the full shear wall is not considered “squat”, an individual storey may have a height to length aspect ratio less than 1. In this case, it is important to change the total height to match the height of the full shear wall so that MASS doesn’t treat the individual storeys as squat shear walls. By default, the total height is set to the same value as the shear wall height so if it is unchanged, there may be an unnecessary reduction in moment resistance.

A full article explaining the difference between “Height” and Total Height” can be found here, including examples showing between 15% to 24% of moment resisting performance losses for not taking the total height into account.

End Fixity

When looking at a shear wall element within a larger shear wall, the objective is to take all aspects of being part of a larger shear wall into account. While there is an option in MASS to fix the top of a shear wall from rotating, the effect on the design can be seen in the difference in bending moment profile below:

Applying a rotational fixity at the top of the wall effectively divides the moment between the top and the bottom of the wall’s supports. While the “Fixed (R)” end condition was added to MASS for the purpose of shear wall designs with significant masonry above which prevent rotation, the scenarios where it is appropriately used would more closely resemble what is pictured below, taken from section 5-7 of the MASS Help files:

As a result, there is no need to change the end fixity of the top of the shear wall, as long as the loads have been properly distributed. Using the cantilever configuration for a multi-storey shear wall , it can be designed element-by-element, accurately designing each storey for the same shear and moment profile as would be used if the full multi-storey shear wall were designed at once.

Only by using the default cantilever fixity selection can an individual storey be adequately modeled without having to apply additional loads to cancel out the effect from a fixed top rotational end condition.

Summary

To quickly summarize, there are three main things to consider when designing a multi-storey shear wall using MASS:

1. Load Distribution: all loads not applied directly to the storey being considered must have their effects included. In particular, the accumulation of axial loads, lateral loads, and overturning moments due to loads applied from storeys above.
2. Total Height: To avoid being penalized for squat shear wall moment arm reductions, be sure to change the total height in order to accurately reflect the full height of the wall.
3. End Fixity: While it may at first seem reasonable to factor in the rotational stiffness from storeys above by changing the top fixity to Fixed (R), it will not result in a moment profile that accurately reflects the moments experienced by the storey in question. The default cantilever selection with properly distributed overturning moments is a more appropriate selection.

The MASS software is a product of a joint partnership between CMDC and CCMPA. CMDC is the authorized provider for MASS Technical Support.

Keywords:      Seismic, Shear Walls, Boundary Elements, Dynamic Loads, McMaster University

Page Content:

Lead Investigators:     Wael El-Dakhakhni (McMaster), Robert Drysdale (McMaster)

CMRC Support:         CMRC members have provided support through the donation of a Commercial Grade Block Machine as well as through the funding and supervision of NSERC Industrial Postgraduate Scholarships (IPS) and the provision of mason time. Continued support is also offered through the formation of the Martini, Mascarin and George Chair in Masonry Design at McMaster University.

• NSERC IPS Student Kevin Hughes (Plastic hinge length and prediction of ductility of masonry shear walls)
• NSERC IPS Student Musafa Siyam (Seismic performance parameters of slender and squat reinforced concrete masonry)
• NSERC IPS Student Ahmed Ashour (Slab coupling effects on the seismic response of reinforced masonry buildings)
• NSERC IPS Student Mohamed Ezzeldin (Seismic performance of coupled reinforced masonry shear walls with boundary elements)

Impacts of Research:            Results generated from this project will help to quantify the behaviour of masonry structures and enable designers to take advantage of aspects of wall coupling and gain a better understanding of system-level seismic performance.

References:

Journal Papers:

Siyam, M., El-Dakhakhni, W., Banting, B., and Drysdale, R. (2015). “Seismic Response Evaluation of Ductile Reinforced Concrete Block Structural Walls. II: Displacement and Performance–Based Design Parameters.” J. Perform. Constr. Facil. , 10.1061/(ASCE)CF.1943-5509.0000804 , 04015067.

Siyam, M., El-Dakhakhni, W., Shedid, M., and Drysdale, R. (2015). “Seismic Response Evaluation of Ductile Reinforced Concrete Block Structural Walls. I: Experimental Results and Force-Based Design Parameters.” J. Perform. Constr. Facil. , 10.1061/(ASCE)CF.1943-5509.0000794 , 04015066.

Heerema, P., Ashour, A., Shedid, M., and El-Dakhakhni, W. (2015). “System-level displacement- and performance-based seismic design parameter quantifications for an asymmetrical reinforced concrete masonry building.” ASCE Journal of Structural Engineering, 10.1061/(ASCE)ST.1943-541X.0001258 , CID: 04015032.

Heerema, P., Shedid, M., and El-Dakhakhni, W. (2014). “Seismic response analysis of a reinforced masonry asymmetric building.” ASCE Journal of Structural Engineering, CID: 04014178.

Kasparik, T., Tait, M.J., and El-Dakhakhni, W.W. (2014). “Seismic performance assessment of partially grouted nominally reinforced concrete masonry structural walls using shake table testing.” ASCE Journal of Performance of Constructed Facilities, Vol. 28, No. 2, 216-227.

Mojiri, S., El-Dakhakhni, W. W. and Tait, M. J. (2014). “Seismic fragility evaluation of lightly reinforced concrete-block shear walls for probabilistic risk assessment.” ASCE Journal of Structural Engineering, CID: 04014116.

Mojiri, S., El-Dakhakhni, W. W. and Tait, M. J. (2014). “Shake table seismic performance assessment of lightly reinforced concrete block shear walls.” ASCE Journal of Structural Engineering, Vol. 141, No. 2, CID: 04014105.

Mojiri, S., Tait, M. J. and El-Dakhakhni, W. W. (2014). “Seismic response analysis of lightly reinforced concrete block masonry shear walls based on shake table tests.” ASCE Journal of Structural Engineering, Vol. 140, No. 9, CID: 04014057.

Conference Papers:

Ashour, A., Heerema, P., Shedid, M. and El-Dakhakhni, W. (2014). “Digital image correlation for damage state identification in reinforced masonry buildings.” Proceedings of the 9^th International Masonry Conference, Guimaraes, Portugal.

Heerema, P., Shedid, M. and El-Dakhakhni, W. (2014). “Response of a reinforced concrete block shear wall structure to simulated earthquake loading.” Proceedings of the 9^th International Masonry Conference, Guimaraes, Portugal.

Siyam, M., El-Dakhakhni, W. and Drysdale, R. (2013). “Ductility of coupled reinforced masonry shear walls.” Proceedings of the 12^th Canadian Masonry Symposium, Vancouver, BC, Canada.

Heerema, P. and El-Dakhakhni, W. (2012). “System-level seismic performance assessment of reinforced concrete block wall buildings, phase I: coupling prevented, torsion allowed.” Proceedings of the 15^th International Brick and Block Masonry Conference, Florianopolis, Brazil.

Mojiri, S., Tait, M. and El-Dakhakhni, W. (2012). “Shake table testing and analytical modeling of fully-grouted reinforced concrete block masonry shear walls.” Proceedings of the 15^th International Brick and Block Masonry Conference, Florianopolis, Brazil.

Siyam, M., El-Dakhakhni, W. and Drysdale, R. (2012). “Seismic behavior of reduced-scale two-storey reinforced concrete masonry shear walls.” Proceedings of the 15^th International Brick and Block Masonry Conference, Florianopolis, Brazil.

Heerema, P., Siyam, M. and El-Dakhakhni, W. (2011). “Proposed system-level testing of multi-storey reinforced masonry buildings under simulated seismic loading.” Proceedings of the 11th North American Masonry Conference, Minneapolis, MN, USA.

Hughes, K., El-Dakhakhni, W. and Drysdale, R. (2011). “Behaviour of reduced-scale reinforced concrete-block shear walls and components.” Proceedings of the 11th North American Masonry Conference, Minneapolis, MN, USA.

Wierzbicki, J., Drysdale, R. and El-Dakhakhni, W. (2011). “Behaviour of reduced-scale fully-grouted concrete block shear walls.” Proceedings of the 11th North American Masonry Conference, Minneapolis, MN, USA.

Banting, B., Heerema, P. and El-Dakhakhni, W. (2010). “Production and testing of ⅓ scale concrete blocks.” Proceedings of the 8^th International Masonry Conference, Dresden, Germany.

Theses:

Mojiri, S. (2013). Shake Table Seismic Performance Assessment and Fragility Analysis of Lightly Reinforced Concrete Block Shear Walls. Master of Applied Science – Thesis, Department of Civil Engineering, McMaster University, Hamilton, ON.

Hughes, K. (2010). Behaviour of Reduced-Scale Reinforced Concrete Masonry Shear Walls and Components. Master of Applied Science – Thesis, Department of Civil Engineering, McMaster University, Hamilton, ON.

Wierzbicki, J. (2010). Behaviour of Reduced-Scale Fully-grouted Concrete Block Shear Walls. Master of Applied Science – Thesis, Department of Civil Engineering, McMaster University, Hamilton, ON.

Vandervelde, J. (2010). Wierzbicki, J. (2010). Behaviour of Reduced-Scale Fully-grouted Concrete Block Shear Walls. Master of Applied Science – Thesis, Department of Civil Engineering, McMaster University, Hamilton, ON.

Kasparik, T. (2009). Behaviour of Partially Grouted Nominally Reinforced Masonry Shear Walls Under Dynamic Loading. Master of Applied Science – Thesis, Department of Civil Engineering, McMaster University, Hamilton, ON.

1. Associate Professor, School of Civil Engineering, Harbin Institute of Technology Harbin, Heilongjiang, 150090, China, xmzhai@hit.edu.cn
2. Senior lecturer, Centre for Infrastructure Performance and Reliability, School of Engineering, The University of Newcastle Newcastle, NSW, 2308, Australia, Yuri.Totoev@newcastle.edu.au
3. Professor, Centre for Infrastructure Performance and Reliability, School of Engineering, The University of Newcastle Newcastle, NSW, 2308, Australia, ,Mark.Stewart@newcastle.edu.au

ABSTRACT

A reinforced grouted concrete block wall/beam, composed of cast-in-place concrete beam and reinforced grouted block wall, is common in mixed retail/commercial and residential construction in China. Often the ground floor houses a shop and commercial storage and residential flats are built on the floors above. In such buildings the ground floor is built as a reinforced concrete (RC) frame with or without shear walls and the upper floors are built with walls of reinforced grouted concrete blocks. According to Chinese code, the RC beam depth to span ratio for wall/beam composition should be greater than or equal to 1/6 for seismic design. Compared to a RC beam with unreinforced masonry (URM) wall on top of it, the reinforced grouted concrete block wall/beam structure has greater stiffness. The higher stiffness can help reducing the cast-in-place RC beam depth to span ratio, and thus increase the height of the ground floor. In this paper, test results for six different wall/beam compositions are presented. The structural capacity, the load-deformation relationship, force-transferring path, and failure mode are examined. The experiments show that the reinforced block wall/beam acts like a deep beam. It was found that the RC beam depth to span ratio can be reduced from 1/6 to 1/10.5.

KEYWORDS: reinforced grouted concrete block, wall/beam, depth to span ratio

B8-1

1. Associate Professor, Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur, UP 208016, India, dcrai@iitk.ac.in
2. Graduate Student, Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur, UP 208016, India, komaraneni1984@gmail.com
3. D. Student, Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur, UP 208016, India, singhal@iitk.ac.in

ABSTRACT

Half-scaled clay brick infill masonry panels were subjected to a sequence of slow cyclic in-plane drifts and shake table generated out-of-plane ground motions to assess the interaction of in-plane damage over the out-of-plane behaviour. The results show that the infill panels maintained structural integrity and out-of-plane stability even when severely damaged; and out-of-plane failure may not be because of excessive inertial forces only but can be due to large out-of-plane deflections. Also, the weaker interior grid elements which divide the masonry in smaller subpanels were able to delay the failure by controlling out-of-plane deflection and significantly enhancing in-plane response.

KEYWORDS: Masonry, infills, stability, seismic response

A8-2

¹Managing Director, NNC Consultant Pvt. Ltd., B-2, Jaswant Chambers, Okhla, Jamia Nagar, New Delhi-110025, India.

²Professor, Civil Engg. Department, Indian Institute of Technology, Delhi, New Delhi-110016, India.

ABSTRACT

A series of laboratory tests has been conducted to investigate the influence of bed joint orientation on interlocking grouted stabilised sand-flyash brick masonry under cyclic compressive loading. Five cases of loading at 0⁰, 22.5⁰, 45⁰, 67.5⁰ and 90⁰ with the bed joints are considered. The brick units and masonry system developed by Prof. S.N. Sinha is used in present investigation. Eighteen specimens of size 500 mm x 100 mm x 700 mm (19.68 in. x 3.94 in. x 27.55 in.) and twenty seven specimens of size 500 mm x 100 mm x 500 mm (19.68 in. x 3.94 in. x 19.68 in.) are tested. The loops of stress-strain hysterisis obtained from cyclic loading tests have been used to determine the energy dissipation characteristics of interlocking grouted stabilised sand-flyash brick masonry. The variation of envelope strain, common point strain and stability point strain with plastic strain has been plotted. A polynomial formulation is proposed for the relations between energy dissipation ratio versus envelope strain and energy dissipation ratio versus residual strain. These relations indicates that the decay of masonry strength starts at about 0.42 to 0.75 times of peak stress depending upon the load case.

KEYWORDS: Interlocking brick, grout, uniaxial, cyclic loading, envelope curve, common point, stability point, stress-strain hysteresis

B6-2

1. Professor, Department of Engineering, Pontifical Catholic University of Peru, Av. Universitaria 1801, Lima 32, Peru, asanbar@pucp.edu.pe
2. Civil Engineer, Pontifical Catholic University of Peru, edelgado@gym.com.pe
3. Professor, Department of Engineering, Pontifical Catholic University of Peru, Av. Universitaria 1801, Lima 32, Peru, dquiun@pucp.edu.pe

ABSTRACT

Many traditional adobe houses located in the Andean highlands are seismically vulnerable due to lack of reinforcement. Of these houses, many have two or more stories, which makes them even more vulnerable. A research project was conducted applying well known confined masonry walls concepts used with clay bricks, now to adobe masonry. A two story full size model was constructed and tested at the Structures Laboratory of the Pontifical Catholic University of Peru. The model was designed using low resistance concrete with minimum reinforcement in the confinement elements. Horizontal bars were also used as reinforcement in the first story.

Several tests, which are common for brick masonry specimens, were also performed on adobe specimens. These included compressive resistance of adobe units, axial compression on small prisms and diagonal compression on small square walls to obtain the shear resistance.

The two story model was tested on a shaking table under horizontal movements of increasing amplitude, completing a total of 5 steps until partial collapse. The behavior observed was good in some aspects, such as shear capacity and adequate flexural resistance to out of plane forces in the first story, horizontally reinforced with steel bars. However, the walls of the second floor, without horizontal bars, had a partial collapse due to out-of-plane forces, indicating that some other aspects have to be improved.

KEYWORDS: confined adobe, confinement, adobe, shaking table, reinforcement, out-of-plane

B6-1