Poisson's Ratio for Materials

Definition:


Poisson's Ratio is the ratio of the transverse to the longitudinal strains under axial stress within the elastic range. It is a negative ratio.

Compression Flange of Beam or Girder

Definition

The widened portion of a beam or girder, such as the horizontal portion of the cross section of a simple-span T-beam, which is shortened by bending under a normal load is known as Compression Flange.

In a continuous floor beam under gravity loading, the laterally un-braced bottom flange is subjected to compressive stresses (Compression Flange) near the interior support(s). To prevent lateral buckling of the flange, this region must be adequately designed.

Related Question:

• What is compression flange?
• Why compression flange is important?
• Which portion of beam or girder is known as Compression Flange?
• Why compression flange must be adequately designed?

Slender Beam

The Slender beam can be defined as the beams in which the spacing of the lateral support to the compression flange or face is more than 50 times the least width of the flange or face.

Since lateral support equal to a minimum of 2 percent of the total (internal) compression in the compression flange is usually considered adequate, and may often be satisfied by simple friction of separate floor materials transmitting the load to the beam, the beam slenderness problem will be encountered only rarely in routine design. It may arise in design of long span upturned roof beams or in the design of thin deep panels used as spandrel beams. Such spandrels are often precast and added to the frame as simply supported beams with a span equal to the column spacing and width of the compression flange as little as 4 inch.

When a slender beam condition arises, the simple solution is to provide lateral bracing within the spacing limits, thus eliminating the condition. Where lateral bracing is impracticable, the load capacity must be reduced.

**Hansel. William, and Winter. George, "Lateral Stability of Reinforced Concrete Beams", ACI Journal, 56(Sep.1959), 193-214.
** Sant. J., and Bletzacker. R. W., "Experimental study of Lateral Stability of Reinforced Concrete Beams", ACI Journal, 58(Dec. 1961), 713-736.

Basic Steps of Building a Foundation

Survey and Stake

Before any construction can begin, the home site is surveyed to establish the home's basic footprint and to ensure the home is set back the appropriate distances from the property lines. The corners of the home are marked by surveyor's stakes. Offset stakes, which are about two feet out from the surveyor's stakes, also are placed. The excavator will dig at the offset stakes, creating a slightly larger hole than the foundation actually will occupy. The extra room enables crews to work on the exterior of the foundation walls.

Excavation

The depth of the excavation is determined by a structural engineer who considers the soil, the frost line and the height of the water table (the depth in the soil at which you find water). Surface soil is removed to expose soil that is compacted enough to bear the load of the home. The excavation must be deep enough to place the top of the footing below the frost line. This prevents the concrete from cracking due to the freeze-thaw cycle of the surrounding soil. The excavation cannot be so deep that it's below the water table, however, because that can cause a chronically wet or flooded basement.

Footings

Footings are poured concrete pathways that help to spread the weight of the home from the foundation walls to the surrounding soil. Footings are wider than the foundation walls they support, and form the perimeter of the home. Sometimes, additional footings are added inside the perimeter to support load-bearing interior walls.

Sub-slab Systems

Plumbing lines are run from the street to the home's basement, by going under or over the footing. In some regions, soil gas mitigation systems are added to collect the soil gases trapped under the slab and vent them to the outside. Eventually, these systems will be covered with the poured concrete slab that is the basement floor.

Foundation Drainage Tile System
This system collects subsurface water and moves it away from the foundation. Foundation drainage tile consists of a continuous run of perforated drainage pipes embedded in gravel along the outside perimeter of the footings.
Some building codes require drainage pipes along the inside perimeter of the footings as well.

Sump

In regions where the earth is flat or the soil tends to be wet, a sump may be added to help collect subsurface water. A sump pump moves the collected water away from the home.

Walls

Foundation walls are constructed by pouring concrete between sets of form work (the total system of support assemblies for freshly poured concrete, including mold, hardware and necessary bracing.) Once the concrete gains its full strength, the form work is removed. Foundation wall thickness is determined by a structural engineer who considers the height of the wall and the load it has to bear. (Structural load is the force or combination of forces of gravity, wind, and earth that acts upon the structural system of a home). Wall thickness varies from home to home, and even within a home.

Anchor Bolts

Anchor bolts are embedded at pre-determined points along the top of the foundation walls. They'll be used during framing to secure the framing to the foundation.

Beam Pockets

Beam pockets are cast in the top of the foundation walls to receive, support, and hold beams in place.

Dampproofing and Waterproofing
A dampproofing or waterproofing seal is applied to the exterior of the foundation walls that eventually will be below-ground. This slows or stops water from traveling through the walls and into the basement.

Slab

A 3-inch to 4-inch thick concrete slab is poured between the walls. The slab helps to stabilize the base of the foundation walls, and also forms the basement floor.

Backfill

Backfill is pushed into the trenches around the exterior of the foundation walls, burying a portion or all of the walls below the surface for added stability. Ideally, backfill is soil that drains easily.

Chain Survey

Chain survey/surveying is an very old method of Surveying. This article includes definition of chain survey along with all detailed information with necessary images about various aspects of chain surveying. 

Chain survey is the simplest method of surveying. In chain survey only measurements are taken in the field, and the rest work, such as plotting calculation etc. are done in the office. Here only linear measurements are made i.e. no angular measurements are made.This is most suitable adapted to small plane areas with very few details. If carefully done, it gives quite accurate results.

The necessary requirements for field work are

• Chain
• Tape 
• Ranging Rod 
• Arrows 
• Cross staff

Suitability of Chain Survey

Chain survey is suitable in the following cases:

1. Area to be surveyed is comparatively small
2. Ground is fairly level

Prestressed Concrete

          Prestressed concrete, the improved condition of RCC (Reinforced cement concrete) where steel is used as both compression and tension member.

       Prestressed concrete is used in structure where higher load is to be sustained such as bridge, arch structure etc. Addition bars are used in tension face of Reinforced Cement Concrete (RCC) member which kept upon tension at the beginning of casting. After casting of the member the tension is to be cut of which tends to compress again. Thus extra compression is imposed on the tension face of the member which eventually increases the tension capacity of the member. Thus, the basic difference between RCC member and prestressed member is that, addition compression is added in the tension face which rises the capacity then simple RCC member. Thus the concrete is prestressed.


keyword:  prestressed concrete beams prestressed prestressing pre stressed prestress pre stress prestressing

Reinforced Concrete

 

 

What is Reinforced Concrete

Concrete is the combination of aggregate and cement where cement is used as the binding material between the aggregates. This combination has got high compressive strength along with very low tensile strength. But structure members also need to sustain in tensile stresses. For an example, a beam in a building undergo both tension and compression. Compression arises on the upper face of the beam whereas tension develops in the bottom face.
If only cement concrete is used that will be good enough to withstand the compression but as it cannot take tension, failure will be initiated in the bottom face. Eventually, the total failure of the member will occur. To reduce this problem, steel bar is inserted on the tension zone of the member as steel has got very high tensile strength. Now the member can now resist compression and tension in combination of steel and concrete as the compression will be taken by concrete on the upper face and tension will be taken by steel on the lower face. Whole system will behave as one in resisting loads of the structure and the concept of reinforced concrete arises. So the reinforced concrete or reinforcement concrete is defined as the combination of steel and concrete which can take both tension and compression arises in a member as one.


For a strong, ductile and durable construction the reinforcement needs to have the following properties at least:

• High relative strength 
• High toleration of tensile strain 
• Good bond to the concrete, irrespective of pH, moisture, and similar factors 
• Thermal compatibility, not causing unacceptable stresses in response to changing temperatures. 
• Durability in the concrete environment, irrespective of corrosion or sustained stress for example. 

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.




 Related Posts:

• Pushover Analysis/ Seismic Analysis of Structures
• Use of Pushover Analysis Results

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

Use of Pushover Analysis 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