Field Measurement Process for modelling of masonry infill walls
Project description
* Type of data needed (story drifts, ambient vibration, other NDT Tests) [Link data to Type of Analysis and Expected Outcomes]
* Determine natural period by using ambient vibration (use fast fourier transform Structural dynamics and modelling)
* Risk assessment for experimental work
Research Proposal
Abstract (Wk 11)
Introduction (Wk 11)
Observations of RC frame with masonry infill buildings
• Hermanns et.al (2013) – Lorca earthquake
• Christchurch earthquake
• Nepal earthquake
Because masonry infill walls are classified as non-structural components, their form can be readily altered during design or renovation works without consideration been given to its effect on the behavior of the structure.
P-Q-R
P. The effect of masonry infill walls on the dynamic behaviour of buildings under earthquake loads is not well understood. This study aims to apply modelling techniques to low rise and high rise reinforced concrete (RC) frames with unreinforced masonry perimeter infill walls. The behaviour of the building will be compared to a frame without the infill wall.
Q. The Redmond Barry building, located on the city campus of The University of Melbourne, has been earmarked for analysis. A structural model would be made on a structural analysis program using structural details sourced from the Property Services department at the university. The behaviour of the building will be determined for various earthquake loads. The model will be calibrated by comparing it with measurements obtained by field testing.
R. Although unreinforced masonry infill walls are no longer common in newer buildings in Australia, there are existing buildings with infill walls. Additionally, this is a common method of construction in developing countries because of its relatively lower construction costs. The findings from this project would provide a deeper understanding of the behaviour of reinforced concrete framed buildings with masonry infill walls and inform the design and retrofitting of existing buildings.
Something in general about presence of infill walls in Australian buildings
Need for the research
How the outcomes will add new knowledge to the topic and help society.
Briefly mention methodology and expected outcomes.
Literature Review (finished by Week 9 Sunday 10/05)
Construction Methods (1-2 page excluding figures)
James – construction of infill walls in Australia. Gap between the frame and the wall. Standards which specify? Look at the Redmond Barry plans and identify construction methods.
Construction methods and the choice of materials involved with constructing masonry infill walls affect the level of interaction with the frame and alter the overall dynamic behavior. (Nwofor)
Asteris et al investigated the failure modes of infilled frames, identifying differing strengths in masonry infill panels and frame members as causes for various failure modes. They also refer to recent research by Zarnic et al 2001, moghaddam, 2004; Rodrigues et al, 2008; Dolsek and Fajfar, 2008; Kose, 2009 showing strong interaction between frame and infill due to influence by the strength properties of the masonry. Research conducted in these papers involves the construction of frames with and without infill, with differing masonry units and mortar and observing the results of failure.
Boral lists stretcher or running bond as the most common bond, and when following the mortar joints, has the longest vertical pathway increasing bending strength. (BORAL). Running bond pattern is used when a wall with one brick width is necessary.
Murty and Jain tested frames containing unreinforced masonry, reinforced masonry and a bare frame. In their research they observed different modes of failure with different sized masonry units, as well as the weakening of the infill due to a larger ratio of mortar thickness, with reduced lateral stiffness being observed. The experimentation involved the construction of scaled walls amongst a frame, to perform a shake table test. It used a scale of 1:2.7 for the frame, 1:2 for burnt-clay brick, and varied the panels with scaled bricks and full scale bricks. The results showed a difference in failure method between scaled-bricks and full-scale bricks showing weaker infill using smaller masonry units, which is linked to the increased ratio of mortar to brick.
Shuklas’ comparative analysis supports the use of larger masonry units, especially autoclaved aerated concrete blocks as they perform better under earthquake loading, are easier to work with and have a lower dry density. However, Al chaar refers to study by Benjamin and Williams (1958) stating brick size was unimportant, and through conducting his own study finds that important factor is the combined compressive and shear strength of the masonry as a whole.
Masonry units generally used in Australia as listed by the Clay Brick and Paver Institute include fired clay brick, concrete block, calcium silicate and natural stone. With varying strengths they are utilized for differing applications. Murty and Jain , as well as Dorji, investigate the different failure modes of infill walls with weak and strong infill, and explain that when masonry infill is present, a reinforced concrete frame begins to act as a truss, with increased axial load in beams and columns, and the formation of a diagonal strut in the infill. Their research shows that strong infill develops a diagonal cracking, while weak infill will fail due to corner crushing, or horizontal shear sliding. (Dorji) He goes on to mention mortar joins are generally the planes of weakness due to low shear resistance.
Block masonry units are hollow as opposed to clay bricks, which are solid. They are also considerably larger and are able to contain reinforcement. When constructing the wall, solid bricks are laid on a full bed of mortar, where as hollow units lay on a face shell mortar bed, reducing the bond strength (Clay Brick and Paver Institute). Compressive strength of units is around 20-100MPa for fire clay bricks, 10-30MPa for concrete blocks, and calcium silicate, 3-5MPa aerated concrete units. Their strengths are found by using tests abiding by AS/NZS 4456.4 (Austral)
Mortar is the most critical component of masonry infill walls and has a strong influence on strength and durability (Dorji). Mortar is made with a combination of sand, a binder and water. Lime mortar is a popular binder to be used in Australia.
Tusinni and Willam evaluated masonry infill properties, and their investigation of over 50 sands around Australia stated the impact on strength was due to water content. Their research goes on to state a lower water/cement ratio leads to a stronger mix. Tusinni and Willam refer to Sarangapani, Reddy and Jagadish 2005, 1998, Yang and Ran research showing there is an increase in compressive strength when there is a lower sand proportion and higher cement content. Cemex Mortars’ education guide to properties of masonry mortar state that higher cement content in mortar creates a higher bond strength between the masonry units. Failure of masonry infill walls is usually through the mortar, as its strength is considerably less than the masonry unit. The bond between mortar and unit can vary from 0-1MPa, however in calculations flexural tensile strength is assumed to be 0.2MPa from AS3700. Batching is used onsite to determine the appropriate mix of mortar (Austral)
Madia and Parsekian mention that a gap is left between the top of the masonry infill and the beam, allowing free deflection for the beam, although common practice in local construction is to fill the gap with a weak mortar. They refer to research done by Dawe (1989) saying the strength of the infilled frame with an upper gap is 50% lower than a frame without a gap. To connect the infill wall with the frame, steel ties are used to connect the non-load bearing wall to the reinforced concrete frame. Steel ties are necessary as masonry is brittle with limited tensile strength. AS2699.1 controls the design and use of wall ties for masonry construction in Australia, and AS3700 governs their durability. Gaps are left to cater for expansion, moisture movements and the deflections of adjacent structures. (Clay Brick and Paver Institute)
Overall effect of infill walls (2-3 pages excluding figures)
Nikeesh – overall effect of infill walls on dynamic (look at the parameters that have been varied). What relationships have researchers come up with to date. Parameters to look for are uneven distribution of walls in the frame, height of building, dimensions of building/ wall. What do these changes result in – changes in stiffness, natural period, mode shapes etc
•Compare and contrast different authors’ views on an issue
•Group authors who draw similar conclusions,
•Criticise aspects of methodology,
•Note areas in which authors are in disagreement,
•Highlight exemplary studies,
•Identify patterns or trends in the literature
•Highlight gaps in and omissions in previous research or questions left unanswered
•Show how your study relates to previous studies,
•Show how your study relates to the literature in general,
•Conclude by summarising what the literature says.
Experimental Observations
Effect of infill wall on the ductility and behavior of high strength reinforced concrete frames
(Essa et. Al, 2013) conducted experimental study on the behavior and ductility of high strength frames with infill walls under the effect of cyclic loading. The parameters that were varied in the experiment included changing the frame from bare frame to infill frame, varying the thickness of the infill as well as the type of masonry units. It was observed that the lateral load resistance on infilled frames were greater than the bare frame however the ductility showed the opposite trend. It also showed that energy dissipation was higher in infill frames compared to bare frames.
Full-scale experimental study on masonry infilled RC moment-resisting frames under cyclic loads
Jiang, Liu and Mao (2015) studied the interaction between masonry infill walls and reinforced concrete frames by carrying out full-scale experimental. Seven specimens were studied of which five specimens had masonry infill walls with a flexible connection to the reinforced concrete frame, one specimen had a rigid connection and one specimen without an infill wall. It was found from the experiment that there was a significant increase in the lateral strength, stiffness and energy dissipation capacity of reinforced concrete frames where the masonry infill wall was rigidly connected to the frame compared to when it was flexibly connected. The displacement ductility ratio of the frame however dropped significantly.
Distinct failure modes were observed in the experiment. The bare frame specimen demonstrated a ductile failure where flexural cracks appeared at the beam ends and a horizontal crack at the bottom of the column. This meant that plastic hinges formed and the failure was ductile. For the specimens with the infill walls, a different failure mode was observed. Initial cracking was observed in the column wall interface and subsequently diagonal cracks formed in the wall. Additionally, large slipping was observed between the masonry units and the mortar. With flexible connection, the infill wall was intact for a longer period of loading.
On the basis of an analytical study of the seismic performance of masonry-infilled RC-framed structures, Kappos (2000) found that taking into account the infill in the analysis resulted in an increase in stiffness by as much as 440%. Depending on the spectral characteristics of the design earthquake, the dynamic behavior of the two systems in study (bare versus infilled frame) can be dramatically different. Kappos also presented a very useful global picture of the seismic performance of the studied infill frames by referring to the energy dissipated by each component of the structural system. At the serviceability level, 95% of the energy dissipation is taking place in the infill walls (subsequent to their cracking), whereas at higher levels, the RC members start making a significant contribution. This is a clear verification of the fact that masonry-infill walls act as a first line of defense in a structure subjected to earthquake load, whereas the RC frame system is crucial for the performance of the structure at stronger excitations (beyond the design earthquake)
Code Approaches
Accounting for the effect of masonry infill walls during structural analysis is a challenging task. National design codes of different countries approach the analysis and design of masonry infill walls in different ways.
2011 Kam, SEISMIC PERFORMANCE OF REINFORCED CONCRETE BUILDINGS IN THE 22 FEBRUARY CHRISTCHURCH (LYTTELTON) EARTHQUAKE
(Table . Summary of contents of national code on masonry infill reinforced concrete frames)
[Talk about the Australian code in this respect.]
Kaushik et al 2006 has highlighted numerous shortcomings in national design codes to adequately consider the effect of MIW on RC frames. These include:
• Lack of information for empirical estimation of natural period of irregular MIW-RC frames.
• Improved design of weak-story frame members is based on formulas and relationships with little rigour.
• No specific treatment on the changing strength and stiffness of MIW-RC frames. This could be attributed to the limited research available as a basis for the formulation for better advice.
• No reliable basis for the estimation of response reduction factor and allowable story drifts that the codes prescribe.
Kaushik et al 2006 highlights that a substantial amount of research is necessary for a better understanding of MIW-RC framed structures so that more informed analysis and design procedures can be prescribed by the various national codes.
Analysis
Since infill walls increases the lateral stiffness and reduces the deformability, the lateral load transfer mechanism is more represented of truss action than frame action (Murty and Jain 2000). This reduces the bending moments in the frame and increases the shear and axial forces.
Masonry infills in reinforced concrete buildings cause several undesirable effects under seismic loading: short column effect, soft-story effect, torsion and out-of-plane collapse.
•Limitations of existing methods
•History and development
•Basic background theory
•Existing application of your experiment and modelling techniques
•Summery connecting into your work
Modelling Method (3-4 pages excluding figures
Yanji – modelling methods. Type of analysis and therefore choice of modelling approach. Macro vs micro
Research Methodology (start Monday Wk 10, finish Wednesday Wk 11)
Analysis (Nikeesh – 2 pages)
• Includes modelling of infill wall
Kim et al 2001 (Experimental study on the material properties of unreinforced masonry considering earthquake load) – equation for elastic modulus of unreinforced brick masonry walls. (properties of diagonal struts)
• linear elastic time history analysis
• parameters to be varied
• software
• loading condition
perhaps use less intensive earthquakes because we are assuming linear THA?
Ko et al 2014 used EL Centro (1940), Taft (1952) and an artificial earthquake created based on design spectrum. The effective PGA of each earthquake was scaled to 0.08g, 0.2g, 0.4g.
Field measurements (Yanji – 2 pages)
Type of data needed (story drifts, ambient vibration, other NDT Tests) [Link data to Type of Analysis and Expected Outcomes]
Determine natural period by using ambient vibration (use fast fourier transform – Structural dynamics and modelling)
Risk assessment for experimental work
!!This is the part that needs to be written!!
Expected Outcomes (Nikeesh)
Critical locations (Where will the masonry fail first?)
Inter-storey drifts
Changes in mode shape, stiffness, natural period)
Timeline/Project plan (James) (finish by Sunday Wk 10)
Gantt Chart (include Semester 1 and proposed Semester 2)
Sourcing of drawings; building information (layout).
Arranging equipment and approvals for field measurements.
Conclusion
Brief conclusion of proposal
Acknowledgement (Wk 11)
Supervisors (Elisa, Massoud)
Graham, Yongping
References (Wk 11)
[use Endnote]