Earthquake

1. Chapter-09Masonry Structures under later loads Siddharth shankar Department of Civil(structure) Engineering Pulchowk Campus

2. F Earthquake Engineering representation of earthquake force • Earthquake cause shaking of ground, so a building resting on it will experience motion at its base. • The roof has a tendency to stay in its original position and the roof experiences a force, called inertia force. • Inertia force is the multiplication of the weight and the acceleration, so larger the weight of the building more the earthquake shaking.

3. Masonry Structures • Masonry is brittle and tensile and shear strength is very low. • Due to Large mass of masonry structures, heavy weight attracts large amounts of seismic forces. • Wall to wall connection and roof connection is generally weak. • Stress concentration occurs at the corners of windows and doors.

4. Failure Modes of a Masonry buildings • Out of plane failure • In plane failure • Diaphragm failure • Connection Failure • Failure due to opening of wall • Pounding • Non-structural component failure

5. Out of Plane Failure • The Earthquake force is perpendicular to the plane. • The wall tends to overturn or bend. • This causes the partial or full collapse of the wall. • This is due to Inadequate anchorage of wall and roof , long and slender wall, etc. • Characterized by vertical cracks at corner, cracks at lintel, roof level and gable wall, etc.

6. In Plane Failure • The Earthquake force is parallel to the plane • The wall is shear off or bend • X- cracks occurs • Characterized by vertical cracks at wall intersection, separation of corners of two walls, spalling of materials, etc

7. Diaphragm Failure • Lack of anchoring produce a push of diaphragm against the wall. • Absence of good shear transfer between diaphragms and reaction wall accounts for damage at corner of wall • Rare phenomenon in the event of seismic motion • Separation of wall and diaphragm cause collapse of buildings

8. Connection failure • For given direction of earthquake, wall A acts as a shear wall and B acts as flexure wall. • If the walls are not tied together wall B overturn (out of olane) and wall A slides (in plane) and collapse occurs. • Masonry units should tied properly

9. Failure due to opening in walls • Opening will obstruct the flow of forces from one wall to another. • Large opening in shear wall reduces the strength of wall against the inertia forces. • Results diagonal cracks in the areas of masonry between opening and cracks at the level of opening. • Thus, openings should small and away from corners.

10. Pounding • When the roofs of two adjacent buildings are at different levels, during earthquake, two buildings strike against each other is called pounding. • Pounding results into cracking of the wall.

11. Non Structural components failure • Falling of plaster from walls and ceiling. • Cracking and overturning of parapets, chimneys, etc. • Cracking and overturning of partition walls. • Cracking of glasses. • Falling of loosely placed objects.

12. Ductile behaviour of reinforced & unreinforced masonry • It is the capacity of an element or structure to undergo large deformation without failure. • Masonry is brittle in nature. • Ductility of masonry structure is governed by the ductility of masonry units & properties of mortar. • Unreinforced masonry cannot withstand tension so cracks develops. • In-plane & out-of-plane failure is also due to ductility of masonry. • To improve ductility reinforcing bars are embedded in the masonry, called reinforced masonry which can resist the seismic force more than unreinforced masonry.

13. Brittle Brittle and Ductile force-deformation behavior Force Ductile Δy Δu Deformation

14. 1. Walls tend to tear apart.

15. 2. Walls tend to shear off diagonally in direction.

16. 3. Failure at corners of walls

17. 4. Walls tend to collapse

18. 5. Failure at corners of openings

19. 6. Hammering/pounding between two adjacent buildings

21. 7. Separation of thick wall into two layers

22. 8.Separation on unconnected wall at junction

23. 9.Seperation of wall from roof

24. Major causes of failure of masonry buildings • Non-integrity of wall floor and roof. • Configuration – irregularity of building causes torsional effect. • Large opening of the building. • Inappropriate position of opening. • Lack of cross wall in large length of wall. • Lack of reinforcement make the masonry building brittle. • Pounding effect. • Lack of anchoring element between two walls.

25. Elements of Lateral Load Resisting Masonry System

26. Horizontal bands for integrity Connecting peripheral walls for structural robustness and integrity • Plinth band • Lintel band • Roof band • Gable band

30. Roof structure • Light and strong roof is desirable. • Secure tiles/slates or use GI sheets. • Good jointing in trusses Concrete floors in 1:2:4 concrete with reinforcement in both directions and bend up near supports.

32. Overall arrangement of masonry structure

33. Chapter-10Testing of masonry elementssiddharth shankarPulchowk Campus Department of Civil Engineering

34. Compressive Strength of Bricks and wall

35. Testing of Wall in compression

36. Diagonal Shear Test

40. Normally carried out:1. Periodically to evaluate the performance of building • 2.To gather information on old building in order to ascertain the methods of repair or to demolish • 3. To ascertain the strength of concrete if cube tests failed.

41. NON DESTRUCTIVE TEST (NDT) • Elastic wave tomography • Rebound Hammer / Schmidt Hammer • Ultrasonic Pulse Velocity • Impact Echo Test • X-Rays • Flat Jack Test

42. Elastic wave tomography • Technique used for locating shallow delaminations, cracks, and voids. • Elastic wave tomography is based on two basic principles from heat transfer: conduction and radiation. Sound materials with no voids, gaps, or cracks are more thermally conductive than materials that are delaminated or contain moisture. • This allows rapid areal mapping of internal conditions. It should be noted that the IT method is most useful for the detection of shallow defects and flaws.   • Tests For: Voids, Cracks, Moisture.

46. Rebound Method • Can be used to determine the in-place compressive strength of concrete within a range of 1500 – 8000 psi (10-55MPa) • A quick and simple mean of checking concrete uniformity. • Measure the distance of rebound of a spring-loaded plunger after it struck a smooth concrete surface. • Results of the test can be affected by factors such as smoothness of concrete surface, size, shape, rigidity of specimen, age & moisture condition. • Type of coarse aggregate & the carbonation of the surface.

47. Nondestructive Test Re-bound hammer Method

48. Nondestructive Test Methods • Rebound Hammer Tests • Schmidt Hammer

49. Rebound Method Using Rebound Hammer

50. Ultrasonic Pulse Velocity • It uses measurement of the speed of ultrasonic pulses through the concrete to correlate concrete strength to standard strength. • Allows the determination of compressive concrete strength and location of cracks. • It will identify non homogenous condition in the structure such as honeycomb, voids and cracks. • Size of cracks can also be determined.