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Technical articles

A group blog by Structural Community in Civil and Structural Engineering

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Use this category to post articles, tips and tricks you've learned. Any topic covering civil & structural engineering is acceptable.

Entries in this blog

Environmental engineering

Activated sludge process (ASP) - biological treatment for wastewater

What is activated sludge? It is a FLOC (i.e. body of micro-organisms gathered in a crowd) produced in a raw or settled sewage by the growth of bacteria and other organisms in the presence of dissolved oxygen and accumulated in sufficient concentrations by returning floc previously formed. Activated sludge process Activated Sludge Process is the biological method for treatment of wastewater. It was devised by Arden and Lockett in 1914. In this process a mixture of sewage and activated sludge is a
Environmental engineering

Live and backfill load on buried sewer pipes

Sewer design requires prior knowledge of soil and site conditions to determine overburden loads that will be placed on buried pipes. Total Load = Backfill Load + Live Load Backfill load (W): It depends upon following factors: Trench Width (B) Depth of Burial i.e., depth of fill above pipe (H) Unit Weight of Fill Material (w) Frictional Characteristics of Backfill Live load: Live Loads on the Surface rarely influence design of sanitary sewer because of their Great Depth and Small Size. Backfi
Geotechnical engineering

Earthquake induced processes

There are generally four types of earthquakes induced processes: 1) Surface rupture, 2) Ground shaking, 3) Ground failure, and 4) Tsunami and Seiches occurrence. Each type has significance to a safe design of structures and is a concern for engineering geologist defining hazard levels. 1. Surface Rupture It is the actual displacement and cracking of the ground surface along a fault trace. Surface rupture is confined to a narrow zone along an active fault. Rupture may happen rapidly during an ear
Structural engineering

Earthquake resistant structures

In countries where earthquakes are of frequent occurrence, important buildings are now designed to withstand all but the most severe shocks. Structures founded on hard rocks are generally less damaged than those on soft grounds and it is found that properly designed steel-framed or ferro-concrete structures possess the highest degree of immunity from damage. Thus, a rigid frame carried on a strong foundation would undergo as a whole the same movement as the ground. In soft ground a concrete raft
Geotechnical engineering

Folds, faults and joints - geological structures

Sedimentary strata may lie horizontal as originally deposited or they may be bent into more or less regular folds, they may be displaced along fractures, or they may be traversed by planes or parting known as joints. Geologic structures influence engineering projects in many ways. Folds and faults obviously have much to do with the selection of dam sites and even such seemingly unimportant matters as the spacing of joints may have vital bearing on uplifting pressure and safety of dams. Gushed an
Surveying

Procedure for leveling

Procedure Suppose A and B are two distance points whose difference of level is to be determined as in the following figure, Place the staff over point A and set up the instrument at suitable distance towards B. The suitable distance between instrument and staff can be about 25 meters. Take a sight on the staff, that reading is called Back Sight (B.S). Now, move the staff to a new position towards B and take the reading, this will be a Fore Sight (F.S). Care should be taken to make the F.S equa
Structural engineering

Types of strain gauges for measurement of strains

Normal Strain Change in the length divided by the original length is called normal strain. Shear Strain Change in angle or shape of to the original angle or shape of the body is called shear strain. Mechanical Strain gauges They can measure the surface strains in any direction. We place gauge parallel to the surface in which direction we want to measure the strains. It can measure static strains only. Optical Strain gauges: In these gauges the measurement and magnification are done optically. A
Geotechnical engineering

Chemical weathering and processes involved in decomposition

Chemical weathering, or chemical decomposition, involves several important reactions between the elements in the atmosphere and those in the mineral of the earth's crust. In these processes, the internal structures of the original minerals are destroyed, and new minerals are formed, with new crystal structures that are stable under conditions at the earth's surface. Water is of prime importance in chemical weathering. It takes part directly in the chemical reaction. It acts as a medium to transp
Geotechnical engineering

Introduction to agents of weathering

All rocks, when exposed for sufficient length of time to the atmosphere, undergo decay from disintegration and decomposition, together referred to as weathering. Disintegration is the break down into small particles by the action of mechanical agents of weathering such as rain, frost etc, decomposition is the breakdown of mineral particles into new compounds by the action of chemical agents such as acid in air and in rain and river water. Denudation is the general term used for the wearing down
Geotechnical engineering

Subsurface investigation - boring and sampling methods

Introduction Accurate and complete subsurface information is necessary for all types of civil engineering projects, for without this information it is not possible to arrive at a rational design for structure and proper construction procedures. Structures have failed because of inadequate or misleading subsurface data, and many so called successful structures could probably have been completed at much less cost because proper consideration have been given to obtaining more complete subsurface in
Surveying

Global positioning system - importance in civil engineering

Object This System provides us with accurate horizontal and vertical measurements and gives us the position of observer in terms of Latitude and Longitude. Advantages This system is fast replacing with conventional methods of surveying like Triangulation, Traversing etc. It no longer requires the inter-visibility of station points. The conventional techniques are still required for detail surveying. The horizontal and vertical control can easily be established with the help of GPS. Instrument
Geotechnical engineering

Introduction to subsidence - evaluating and mitigating its effects

1. Introduction Subsidence is displacement of ground surface vertically over a broad region or at localized areas. It may be either a gradual lowering or a collapse. This can have costly effect on facilities and structures over a subsiding area. Subsidence results from a number of different mechanisms. It can occur as a consequence of natural processes. The dissolving of limestone, salt, or other soluble materials creates underground openings that may collapse. Collapse may also occur in the roo
Surveying

Temporary and permanent adjustments of a theodolite

What is an adjustment? Adjustment of a theodolite means the operation of tightening or loosening of moveable parts to prepare the instrument for accurate measurement. It also includes other operations meant for this purpose. There are two types of adjustments for a theodolite - Temporary Adjustment & Permanent Adjustment. 1 - Temporary adjustments These are required for each setting up of the instrument and includes following, a - Centering This is to center the instrument exactly over the g
Surveying

Surveying types and maps

Surveying Surveying is a technique in by which measurements are taken on the surface of the earth and presented on the maps or stored in the digital format and vice versa. There are following types surveying, 1. Plane surveying It is meant for small areas where the surface of the earth is taken to be plane surface, i.e. curvature of the earth is ignored. e.g. for survey inside a city. 2. Geodetic surveying In this curvature of the earth is taken into consideration. e.g. National surveys, Basic t
Surveying

Aerial and terrestrial photogrammetry

Photogrammetry Photogrammetry is the branch of surveying in which measurements are made from photographs. Merits This is a very quick and accurate method of surveying in which the ground observations are almost totally eliminated. This is very accurate method if true interpretations of photographs are made. It also provides means to develop a Contour map. Demerits This method requires fair weather conditions. The instrument is very expensive, and staff should be highly qualified and experien
Surveying

Open traversing with the help of theodolite

By deflection angle method Bearing of the first line AB is measured with the help of prismatic compass or by any other method. Setup the theodolite and point B and with horizontal circle reading bisect point A. Transit the telescope and rotate it in the direction of next station point C and note the angle, this will be θ1 R and is called deflection angle at B. Repeat this procedure for the remaining points of traverse measuring the deflection angle and writing with them letter "L" or "R". Fo
Surveying

Open and closed traversing with the help of prismatic compass

For open traversing Following procedure is adopted in case of open traversing with the help of prismatic compass, We will setup the compass at point A, B, C and so on and note the Fore Bearing and back Bearing of lines. The length of lines or legs are measured by chain twice and mean lengths are calculated. During taking measurements in the field, the method used angular measurement, and linear measurement should be of same standard of accuracy, i.e. either combination of Prismatic compass an
Surveying

Measurement of vertical angle with theodolite including example

Vertical angle It is the angle in the vertical plane between horizontal line passing through the intersection of cross hairs and inclined line joining intersection of cross hairs and the point being observed. Circle reading in case of vertical angle During Face left vertical angle will be computed in the following manner, When angle of elevation, vertical angle = 90° - Circle reading. When angle of depression, vertical angle = Circle reading - 90°. Now, during Face right vertical angle will b
Surveying

Measuring personal pace length

Introduction Sometimes it needs to approximate the distance between two points. One can do it without using any distance measuring instrument. But firstly, you need to compute your own pace length, then you can use your pace length to approximate the actual distance. However, it is not accurate enough to use into the calculations or computations. Procedure open a chain and let it fly in straight position along the piece of ground. Walk along the chain and count the number of steps. The distanc
Surveying

Linear measurement instruments and their permissible error range

1. Pacing Permissible error ≤ 1 feet in 20 feet. 2. Chain Permissible error ≤ 1 in 1000. 3. Metallic tape Permissible error ≤ 1 in 1000. 4. Steel tape This tape is made of steel alloy of very small co-efficient of thermal expansion. Permissible error ≤ 1 in 1000. 5. Invar tape This tape is made of very expensive steel alloy of almost negligible co-efficient of thermal expansion and is used for very precise linear measurements. Permissible error ≤ 1 in 50,000. 6. Tachometry Permissible error ≤ 1
Surveying

Introduction to leveling

Leveling It is the branch of Surveying in which relative elevations of points are determined. There are following Types of Leveling 1. Ordinary leveling It is general purpose Leveling and unless otherwise stated all types of Leveling will come into this category. 2. Reciprocal leveling This is done when a site is unusually long, i.e. crossing the river. Sights are taken from the two banks by placing the staff on the opposite bank almost simultaneously and finding the average of apparent differen
Surveying

Essential parts of a theodolite

1. Tripod It should be of a rigid type capable of fixing the position of the instrument with a small lateral movement on its top when required. 2. Foot screws These are provided for leveling the instruments. 3. Plate level Provided for checking the level of the instrument. 4. Horizontal clamp Provided to clamp the movement in horizontal plane. 5. Vertical clamp For clamping movement in vertical plane. 6. Slow motion screws These screws are used to move Theodolite either vertically or horizontall
Surveying

Computation of corrected bearings and internal angles

Fore bearing It is the bearing of line when the first letter of line say AB is taken as origin. This is to be written as Fore Bearing (F.B). Back bearing It is the bearing of line when second letter of line say AB is taken as origin and this is to be written as Back Bearing (B.B). Theoretical difference between Fore Bearing (F.B) and Back Bearing (B.B) should be 180°. Local attraction If the difference between magnetic Fore Bearing and Back Bearing of a line is not exactly 180°, it may be due to
Surveying

Closed traversing with the help of theodolite including example

Latitude and Departure In order to do start with Theodolite Traversing you should be familiar with the Latitude and Departure which are discussed briefly below, OA is the line with whole circle bearing equal to θ. OC = Latitude = lCosθ OB = Departure = lSinθ By using the above formulae for Latitude and Departure with whole circle bearing, calculator will be giving algebraic sign automatically for Latitude and Departure. For a closed Traverse ∑ of all Latitude is equal to zero and ∑ of Depart
Environmental engineering

General specifications of pipes being used in water distribution system

The following points should be kept in mind while selecting pipe for a certain water supply system, Carrying capacity. Durability. Fire cost. Maintenance cost. Type of water to be conveyed. 1. Cast iron pipes (C.I) Most widely used for the city water supplies. Average life is 100 years. Corrosion my reduce its capacity by 70%. Must be lined with cement or bitumen. C = 130 for new pipe. C = 100 for old pipe (Selected for Design). "C" is the Hazen Williams Coefficient known as HWC. It i

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