Use of Pushover Results

Pushover analysis has been the preferred method for seismic performance evaluation of structures by the major rehabilitation guidelines and codes because it is 5 conceptually and computationally simple. Pushover analysis allows tracing the sequence of yielding and failure on member and structural level as well as the progress of overall capacity curve of the structure. The expectation from pushover analysis is to estimate critical response parameters imposed on structural system and its components as close as possible to those predicted by nonlinear dynamic analysis. Pushover analyses provide information on many response characteristics that cannot be obtained from an elastic static or elastic dynamic analysis. These are:

• Estimates of inter-story drifts and its distribution along the height.
• Determination of force demands on brittle members, such as axial force demands on columns, moment demands on beam-column connections
• Determination of deformation demands for ductile members
• Identification of location of weak points in the structure (or potential failure modes)
• Consequences of strength deterioration of individual members on the behavior of structural system
• identification of strength discontinuities in plan or elevation that will lead to changes in dynamic characteristics in the inelastic range
• verification of the completeness and adequacy of load path

Pushover analysis also exposes design weaknesses that may remain hidden in an Elastic analysis. These are story mechanisms, excessive deformation demands, strength irregularities and overloads on potentially brittle members.

Limitations of Pushover Analysis

Although pushover analysis has advantages over elastic analysis procedures, underlying assumptions, the accuracy of pushover predictions and limitations of current pushover procedures must be identified. The estimate of target displacement, selection of lateral load patterns and identification of failure mechanisms due to higher modes of vibration are important issues that affect the accuracy of pushover results. Target displacement is the global displacement expected in a design earthquake. The roof displacement at mass center of the structure is used as target displacement.

Pushover Analysis/ Seismic Analysis of Structures

Pushover analysis, a widely used method for seismic performance evaluation of a structure, is a static nonlinear procedure in which the magnitude of the structural loading is incrementally increased in accordance with a certain predefined patterned.

The static pushover analysis is becoming a popular tool for seismic performance evaluation of existing and new structures. The expectation is that the pushover analysis will provide adequate information on seismic demands imposed by the design ground motion on which the structural system and its component.

Software available to perform nonlinear static (pushover) analysis are ETABS, SAP, ADINA, SC-Push3D etc.

 Related Posts:

• Use of Pushover Analysis Results
• Limitations of Pushover Analysis

Keywords: Pushover push over analysis Earthquake performance structure civil engineer engineering rcc steel 

Ferrocement : Introduction, Property & Application

 Ferrocement

Ferrocement, also written as ferrociment, ferrocemento, ferrocimento, and ferrozement, literally mean much steel rather than much concrete. The Committee 549 of the American Institute for Concrete submitted the following definition of the ferrocement subsequently adopted by the majority of the specialists:

     " The ferrocement is a type of reinforced concrete in thin elements currently constituted by micro) concrete of hydraulic cement reinforced with thick layers of continuous netting, in wire with a relatively small diameter. The net may be metallic or in other materials ."

A.E. Naaman defines ferrocement as reinforced concrete in guise of thin elements with

Assumptions of Multi-stored and Multi-bay Frames

Portal Method

1. Point of contra flexure is assumed to be at mid-height of each column.
2.  Point of contra flexure assumed to be at mid-span of each girder or beam. 
3. Horizontal shear on each story is divided between columns in that story such that each interior column carries twice as much shear as exterior Column caries.

Cantilevers Method

1. Point of contra flexure is assumed to be at mid-height of each column. 
2. Point of contra flexure is assumed to be at mid-span of each girder or beam. 
3. Intensity of axial stress in each column of a story is proportional to the horizontal distance from the c.g of all the columns of that story.

Steps of Construction of a Single Footing

The main steps of construction of a single footing are:

1. Excavation


2. Leveling & Dressing


3. Brick Flat Soling (BFS)


4. C.C. Layer


5. C.C. Block


6. Footing Reinforcement


7. Installation of Short Column Reinforcement


8. Formwork/Shuttering


9. Concrete Casting


10. Removal of Formwork


11. Curing


12. Back Filling.

COLUMN FOOTING

Column Footing is also famous as independent footing. An independent footing is one which is provided under a column or either similar member for distributing concentrated load in the form of uniformly loads on the soil below. The footing may be square, rectangular or circular in plan. Depending upon the load to be carried and the bearing capacity of soil, this may be of brick masonry, stone, R.C.C., steel grill-age etc. On account of low bending strength the footings constructed with brick, stone or plain concrete require considerable depth to be safe to carry heavy loads. The depth of plain concrete footing can be appreciably reduced by providing reinforcements at its base to take up tensile stresses. R.C.C. column footings may be circular, rectangular or square in plan. The footing is reinforced both-ways by means of mild steel ribbed bars placed at right angles to one another at equal distances apart.

SHALLOW FOUNDATION

A shallow foundation transfers building loads to the nearest earth surface, rather than to a sub-surface layer or a range of depths as does a deep foundation. Shallow foundations are usually embedded a meter or so into soil. One common type is the spread footing which consists of strips or pads of concrete (or other materials) that extend below the frost line and transfer the weight from walls and columns to the soil or bedrock. Another common type is the slab-on-grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface.

DEEP FOUNDATION

Deep foundations are used to transfer a load from a structure through an upper weak layer of soil to a stronger deeper layer of soil. There are different types of deep foundations including helical piles, impact driven piles, drilled shafts, caissons, piers, and earth stabilized columns. It ensures stability and durability of a structure. Historically, piles were wood, later steel, reinforced concrete, and per-tensioned concrete. Sometimes these foundations penetrate bedrock.