![MASONRY INFILL STIFFNESS VERIFICATION {cont’d}
Infill walls replaced by Equivalent Diagonal Strut.
By determinate the diagonal strut AREA using the brick and masonry
properties, the stiffness of the wall were estimated.
Z= 0.175 [ λ . ℎ)− 0.4
] dm
𝐀𝐞 = 𝐙 . 𝐭
λ =
4 𝐸𝑚 . 𝑡𝑚 . 𝑠𝑖𝑛 (2θ)
4 . 𝐸𝑓. 𝐼 𝑐 ℎ𝑚
Area of STRUT = Width (Z) x Thickness
SLIDING and COMPRESSION SHEAR failure
DISPLACEMENT AT YIELDING
Initial wall Stiffness = 2 x [Min. Initial shear / Displacement]
(Madan et al., 1997)
(Das and Murphy,2004)
(Mainstone,1971)](https://image.slidesharecdn.com/eda6d4ee-e980-4e55-84f9-fda646705bfa-150218115917-conversion-gate02/85/DNV-GL-01-04-2014-7-320.jpg)
DNV - GL 01-04-2014
- 1. ‘Seismic Analysis and Response of Bare Vs. Masonry In-filled Frame Structures’ Researcher: Mr Constantinos Chris Andreou BEng, MSc Civil- Subsea Graduate Engineer
- 2. RESEARCH PROPOSAL Several countries lie in areas susceptible to earthquakes and their structures need to be designed to withstand seismic loads. Infill panels are not considered in the design process but treated as architectural (non-structural) components. This study assessed the seismic performance of RC buildings by utilizing dynamic analysis to obtain predictions of the infill panels used in their design. The present study may assist in reducing risks of collapsed structures in case of earthquake disasters ‘ B a r e f ra m e a n d M a s o n r y I n - f i l l e d s t r u c t u r e s ’
- 3. Research AIMS and OBJECTIVES To analyse and demonstrate the importance of masonry infill walls against seismic loads. To compare the available seismic design methods proposed by Structural Eurocodes. Research on structural seismic performance. Evaluation of structural seismic performance of buildings using linear structural analysis methods proposed by Structural Eurocodes Estimation of Masonry Infill Stiffness. Comparison of Bare and Infilled framed structure using analytical and computer techniques.
- 4. PROPOSED MODELS FOR ANALYSIS Bare Frame Partially-Infilled Fully-Infilled Masonry infill configurations modelling o Medium Class Ductile Reinforced Concrete o Regular building in Plan and Elevation o 6 Stories with known heights o 4 x 4 Frames
- 5. METHODS OF SEISMIC RESPONSE ANALYSIS The following two types of linear-elastic analysis were contacted: I. Equivalent static method {Lateral Force Method} o The system response is derived by applying equivalent lateral seismic load to the model. o These lateral forces are applied as static loads at the position of concentrated mass of the structure at each floor. II. Response Spectrum Method o Is one of the most popular methods in modern earthquake engineering. o Offers logical results and it is more economical. o Requires the determination of a response spectrum from measured seismic activity. ‘Spectral acceleration against Periods’
- 6. MASONRY INFILL STIFFNESS VERIFICATION Infill Wall panels are not included in structural design Such assumption may lead to inaccurate approximation of strength, ductility and stiffness of concrete framed buildings. ‘Research has proved that the i nfi ll system behave as a braced frame with the wall forming ‘co m pressio n stru ts’ Equivalent diagonal compression ‘STRUT’
- 7. MASONRY INFILL STIFFNESS VERIFICATION {cont’d} Infill walls replaced by Equivalent Diagonal Strut. By determinate the diagonal strut AREA using the brick and masonry properties, the stiffness of the wall were estimated. Z= 0.175 [ λ . ℎ)− 0.4 ] dm 𝐀𝐞 = 𝐙 . 𝐭 λ = 4 𝐸𝑚 . 𝑡𝑚 . 𝑠𝑖𝑛 (2θ) 4 . 𝐸𝑓. 𝐼 𝑐 ℎ𝑚 Area of STRUT = Width (Z) x Thickness SLIDING and COMPRESSION SHEAR failure DISPLACEMENT AT YIELDING Initial wall Stiffness = 2 x [Min. Initial shear / Displacement] (Madan et al., 1997) (Das and Murphy,2004) (Mainstone,1971)
- 8. MASONRY INFILL STIFFNESS VERIFICATION There are many investigations and proposed verifications of masonry infill stiffness that impediment to a reliable modeling Limited amount of research has been undertaken on Infilled frames with openings The initial stiffness of the masonry infill panel was defined and used in linear-elastic analysis methods RESULTS TAKEN FROM BARE FRAME AND MASONRY INFILL CASE WERE COMPARED
- 9. • Masonry Infilled Frames and their Seismic Behaviour at Structures Increase Stiffness of structures The fundamental period is decreased The Base Shear is increased The structural system is more reliable at seismic action as part of the load is consumed by the infills Energy capacity of the structure is significantly increased RESEARCH DELIVERABLES Comparison of Displacements of Bare and Infill cases
- 10. Distribution and Comparison of Results Comparison of Seismic Analysis Methods BASE SHEAR (KN) MODEL T = Ct x H3/4 T = 2.(d)^0.5 Bare Frame 373.3 472.60 Partially Infilled F. 373.3 601.50 Fully Infilled 373.3 696.50 o Equivalent Static method 1. Carried out in less time by doing few and simple calculations 2. Temporal variations were neglected. 3. Considers only maximum possible responses. 4. Gives an initial idea for magnitude that will be acted due to a possible earthquake. 1) Consider the Height 2) Lateral elastic displacement (F / k) Can be used for preliminary design situations and for buildings up to 10 storey as mentioned by EC8.
- 11. 0 100 200 300 400 500 600 700 800 900 Bare Frame Partially Infilled Frame Fully Infilled Frame Equivalent static method(T = 2.(d)^0.5) 472.613 601.507 696.482 Response spectrum method 560.82 732.42 819.96 BASESHEAR(KN Equivalent static method(T = 2.(d)^0.5) Response spectrum method o Response Spectrum method Comparison of Seismic Methods {cont’d} 1. Approximates better the fundamental period of vibration (T) 2. Yields more accurate and responsible results 3. Involves simplifying assumptions 4. Errs on the side of safety Difference varies from 15 - 18 % Response spectrum analysis provides significant information about real-world applications when considering a linear, elastic system that is exposed to a forcing function (earthquakes). WASTE OF MATERIALS equal to 15 - 18 %
- 12. Infill Panels Behaviour 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 0 1 2 3 4 5 6 MAXIMUMDISPLACEMENT(mm) FLOOR LEVELS Bare Frame Partially Infilled Frame Fully Infilled Frame Design Codes should NOT neglect the effects of masonry infills • 2 Times smaller (Increase in stiffness) • P.I.F displacement at first and second floor is bigger compared to B.F (Presages Soft storey effect) • F.I.F has very small storey displacements (presence of infill walls) o Displacement
- 13. o Measured Envelope of Base Shear Vs. Displacement 0 20 40 60 80 100 120 140 160 180 200 0 1 2 3 4 5 BASESHEAR(KN) DISPLACEMENT (mm) Fully Infilled Frame Partially Infilled Frame Bare Frame Maximum Displacements at TOP storeys BASE SHEAR (KN) Story Bare Frame Partially Infilled Frame Fully Infilled Frame 0 0 0 0 1 47.441 93.539 77.437 2 60.745 105.405 103.375 3 81.244 122.396 134.377 4 97.656 135.562 158.472 5 123.54 140.127 171.972 6 127.058 133.264 166.855 ΣFBi 537.7 732.4 812.5 • F.I.F presented to be 34% stronger compared to B.F • P.I.F presents 26% difference from B.F • Higher amount of Shear force is needed to displace equal each models top storey. *An estimation of the overall ductility demand can be obtained.
- 14. COMPUTER COMPUTATION TECHNIQUES Using SAP 2000 the RESPONSE SPECTRUM ANALYSIS was carried out for Bare model case. Results were compared to analytical results SAP 2000 (Linear Dynamic Procedure) Model simulation
- 15. o SAP 2000 {cont’d} Story SAP 2000 ANALYTICAL 1 10.3 0.178 0.27 2 18.48 0.319 0.38 3 27.9 0.481 0.527 4 37.19 0.642 0.647 5 50.19 0.866 0.881 6 57.96 1 1 T (s) 0.476 0.488 Story DISPLACEMENT 0 ANALYTICAL SAP 2000 Percentage difference (%) 1 1.118 1.5 25 2 1.576 2.63 40 3 2.185 3.78 42 4 2.682 4.8 44 5 3.654 6.07 40 6 4.147 6.91 40 Base Shear 537.7 363.9 47 The large percentage difference caused from: • The different method of structural element’s stiffness calculation . • The reduction moment of inertia at beams and columns equal to33% and 50% respectively. There is only a 4% variation of results at first vibration mode Vibration mode shapes
- 16. The behaviour of infill frames depends on the properties of infill and frame. The proposal analytical procedure can be implemented in the design and used by available computational tools. Infilled frames can be improved by applying recommended guidelines during their construction to achieve a better behaviour. The non-structural infills walls can change the global seismic behaviour of framed buildings Masonry infill walls have major influence to the structure’s performance ALL project Deliverables were PROVED… CONCLUSION
- 17. REFERENCES I. Structural Eurocodes, 2010. ‘Extracts from the Structural Eurocodes for students of structural design’. Third edition. II. Thesis on ‘Seismic Analysis and Response of Bare and Masonry In-filled Reinforced Concrete Frame Structures’. III. ‘Literature Survey Report’ of thesis.
Editor's Notes
- #7: The method requires the determination of a response spectrum from measured seismic activity. This data is then reduced into a spectrum of seismic action versus natural frequency. Detailed information from the structural model is coupled with the corresponding spectral values for each specific mode of vibration
- #8: infill walls behave as structural components offering further stiffness to the structure