The Creation of the Great Wall of China

Who Built the Great Wall When and Why
Parts of the Great Wall were first built by princes and overlords in the Seventh Century BC as regional border defenses when China was divided into many small states. After the unification of China in the beginning of the Qin Dynasty (221-206 BC), the China's first emperor, Qin Shihuang (you must have heard of his Teracotta Army), linked the walls of the three states in the north (Qin, Zhao and Yan). This formed the first "Wan Li Chang Cheng" (ten thousand li Great Wall, li is a Chinese unit of length, 2 li = 1 km). Read more...

How was the Great Wall Built?
Twisting and turning up mountain and down valleys, the great wall, is really a marvelous civil-engineering project in ancient times. at the time relying solely on the manpower with no help of machinery at all, except such animals like donkeys and goats which were used to carry stone and earth up hills and down dales, it was relly an unimaginably difficult job to carry out such a huge project. Read more...

How Was the Great Wall of China Made?
Construction of the Great Wall of China began around 700 B.C. During this time, China was divided into seven different lands, which began building walls to protect themselves from one another. Within 500 years, the walls stretched over 3,000 miles. About 200 B.C., the Chinese states were united for the first time under Emperor Qin, who began the process of connecting the many different walls to protect China from northern invaders. Read more...

Construction of the Great Wall of China
The final result of the largest construction project in history to be put into effect was a twenty five foot high, twenty foot wide, and over 1500 mile long wall, called The Great Wall of China. The Great Wall of China was made of ear th and stone and was built to protect China from northern invasions. Read more...


Welding Rod Info

1. The E7018 welding rods I've been buying are now marked E7018 H4R. What does the H4R mean? Are these rods different than the E7018 rods I've used before?

H4R is an optional supplementary designator, as defined in AWS A5.1-91 (Specification for shielded metal arc welding electrodes). Basically, the number after the "H" tells you the hydrogen level and the "R" means it's moisture resistant.

"H4" identifies electrodes meeting the requirements of 4ml average diffusible hydrogen content in 100g of deposited weld metal when tested in the "as-received" condition.

"R" identifies electrodes passing the absorbed moisture test after exposure to an environment of 80ºF(26.7ºC) and 80% relative humidity for a period of not less than 9 hours.

The H4R suffix is basically just additional information printed on the rod, and does not necessarily mean a change in an electrode previously marked E7018.

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2. Why is hydrogen a concern in welding?

Hydrogen contributes to delayed weld and/or heat affected zone cracking. Hydrogen combined with high residual stresses and crack-sensitive steel may result in cracking hours or days after the welding has been completed.

High strength steels, thick sections, and heavily restrained parts are more susceptible to hydrogen cracking. On these materials, we recommend using a low hydrogen process and consumable, and following proper preheat, interpass, and postheat procedures. Also, it is important to keep the weld joint free of oil, rust, paint, and moisture as they are sources of hydrogen.

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3. What is the maximum plate thickness which can be welded with Innershield® NR®-211-MP (E71T-11) wire?

NR®-211-MP is restricted to welding these maximum plate thicknesses:

Wire Diameter Maximum Plate Thickness
.030"(0.8mm) 5/16"(7.9mm)
.035"(0.9mm) 5/16"(7.9mm)
.045"(1.1mm) 5/16"(7.9mm)
.068"(1.7mm) 1/2"(12.7mm)
5/64"(2.0mm) 1/2"(12.7mm)
3/32"(2.4mm) 1/2"(12.7mm)
For thicker steels, look to Innershield® NR-212. It has similar welding characteristics to NR®-211-MP but is designed for use on materials up to 3/4" (19.1mm) thick.

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4. What electrode can I use to join mild steel to stainless steel?

Electrode selection is determined from the base metal chemistries and the percent weld admixture. The electrode should produce a weld deposit with a small amount of ferrite (3-5 FN) needed to prevent cracking. When the chemistries are not known, our Blue Max® 2100 electrode, which produces a high ferrite number, is commonly used.

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Welding Rods/ Electrodes Tutorials

There are many different types of electrodes used in the shielded metal arc welding, (SMAW) process. The intent of this guide is to help with the identification and selection of these electrodes.

Arc welding electrodes are identified using the A.W.S, (American Welding Society) numbering system and are made in sizes from 1/16 to 5/16 . An example would be a welding rod identified as an 1/8" E6011 electrode.
The electrode is 1/8" in diameter

The "E" stands for arc welding electrode.

Next will be either a 4 or 5 digit number stamped on the electrode. The first two numbers of a 4 digit number and the first 3 digits of a 5 digit number indicate the minimum tensile strength (in thousands of pounds per square inch) of the weld that the rod will produce, stress relieved. Examples would be as follows:

E60xx would have a tensile strength of 60,000 psi E110XX would be 110,000 psi

The next to last digit indicates the position the electrode can be use in. READ MORE...


All positions
Deep penetration
DC reverse polarity
Rod is mild steel
Application – use medium arc, whipping or weaving on vertical and overhead to control bead sag.


Flat amps

Vertical amps

Overhead amps


50 – 90

50 – 90

50 – 90


90 – 140

90 – 130

90 – 130


120 – 180

130 – 150

130 – 160


150 - 230

140 - 270

140 - 180


Gas Welding Rods come in different forms such as, Aluminum, Bronze Alloy, Carbon Steel, Copper Alloy, Hard Facing and Maintenance Alloy. Manufacturers include ESAB, Harris Welco and Radnor. You'll find all of your gas welding rod needs with Airgas.Aluminum gas welding rod comes in two varieties, bare and flux-cored. Bare is recommended for brazing thin sheets, extruded shapes and especially corner joints. Flux-cored has non-corrosive, non-hygroscopic flux inside a tubular rod; no separate flux required.

Silicon Bronze is a copper based filler metal primarily used for TIG and oxyacetylene welding of copper, copper-silicon and copper-zinc base metals to themselves and to steel. Silicon bronze can be used for on plain or galvanized steel sheet metal. It can also be used for surfacing areas subjected to corrosion. READ MORE...


There are a lot of different welding electrodes and wires out there. In the field, welding electrodes are usually referred to as "welding rods" so I will use that term here.

"Stick Welding" is also the term of choice in the field for SMAW, the acronym for Shielded Metal Arc Welding.

Stick welding used to be done with a bare welding rod. It was very difficult, and could only be used in the flat position. If you've ever stuck a rod with flux on it, you can only imagine how many times they stuck bare rods! If the rod gets too close to the base metal it will decrease the voltage causing the arc to go out. READ MORE...


Steel Tutorials

Both carbon and HSLA steels can be heat treated to provide yield points in the range of 50 to 75 ksi. This provides an intermediate strength level between the as-rolled HSLA steels and the heat-treated constructional alloy steels.

A633 is a normalized HSLA plate steel for applications where improved notch toughness is desired.

Available in four grades with different chemical compositions, the minimum yield point ranges from 42 to 60 ksi depending on grade and thickness.

A678 includes quenched-and-tempered plate steels (both carbon and HSLA compositions) with excellent notch toughness. It is also available in four grades with different chemical compositions; the minimum yield point ranges from 50 to 75 ksi depending on grade and thickness.

A852 is a quenched-and-tempered HSLA plate steel of the weathering type. It is intended for welded bridges and buildings and similar applications where weight savings, durability, and good notch toughness are important.

It provides a minimum yield point of 70 ksi in thickness up to 4 in. The resistance to atmospheric corrosion is typically four times that of carbon steel.

A913 is a high-strength low-allow steel for structural shapes, produced by the quenching and self-tempering (QST) process. It is intended for the construction of buildings, bridges, and other structures.

Four grades provide a minimum yield point of 50 to 70 ksi.

Maximum carbon equivalents to enhance weldability are included as follows: Grade 50, 0.38%; Grade 60, 0.40%; Grade 65, 0.43%; and Grade 70, 0.45%.

 Also, the steel must provide an average Charpy V-notch toughness of 40 ft [1] lb at 70F.


Civil Engineering Tutorials

Virtually all civil engineering structures are unique. They have to be designed for some specific purpose at some specific location before they can be constructed and put to use. Consequently the completion of any civil engineering project involves five stages of activity which comprise the following:

1. Defining the location and nature of the proposed works and the quality and magnitude of the service they are to provide.

2. Obtaining any powers and permissions necessary to construct the works.

3. Designing the works and estimating their probable cost.

4. Constructing the works.

5. Testing the works as constructed and putting them into operation.

There are inherent risks arising in this process because the design, and therefore the estimated cost of the works, is based on assumptions that may later have to be altered.

The cost can be affected by the weather during construction and the nature of the ground or groundwater conditions encountered.

Also the promoter may need to alter the works design to include the latest technical evelopments, or meet the latest changes in his requirements, so that he does not get works that are already out-of-date when completed.

All these risks and unforeseen requirements that may have to be met can involve additional expenditure; so the problem that arises is – who is to shoulder such additional costs?

Clearly if the promoter of the project undertakes the design and construction of the works himself (or uses his own staff) he has to meet any extra cost arising and all the risks involved.

But if, as in most cases, the promoter engages a civil engineering contractor to construct the works, the contract must set out which party to the contract is to bear the cost of which type of extra work required. The risks involved must also be identified and allocated to one or the other party.

Teaching Arches in Structural Analysis Courses Basics and Tutorials Free PDF Download Link

Structural Analysis Tutorials

Abstract - This paper reports on an experience carried out by the author to include the topic of Arches in a course on Structural Analysis II.  The paper shows that the most popular textbooks do not address the topic, by considering the number of pages dedicated to arches.

A strategy was implemented in which the instructor motivated the students to investigate about arches, with emphasis on their structural importance, their historical importance, their present day importance, and their esthetic importance.

The students carried out projects in which the arches were analyzed by means of frame elements. The five structural themes were the numerical modeling of arches using frame elements, analysis of Romanesque and Gothic cathedrals, arch-supported bridge, and arch-suspended bridge. The evaluation of the experience was based on a questionnaire and showed highly positive results.

Arch structures have a double feature in terms of civil engineering education: On the one hand, they have been used throughout the history of architecture as a main structural component. This is also true of present day construction, in which arches play a major role in the design of bridges, some building types, and other structures.

On the other hand, they are neglected by the civil engineering curricula throughout the nation. Arch structures could (and should) be taught in Structural Analysis, a course that is obligatory in all civil engineering programs.

In some schools there are two Structural Analysis courses (at the University of Puerto Rico they are INCI 4021 and INCI 4022, with a total of 6 credits), while other schools teach one course with 3 or 4 credits. First, this paper contains a review of 20 books on structural analysis, in order to show that an average of only 2% of the texts is dedicated to arches.

Second, the paper illustrates the arguments used by this instructor to highlight the historic and contemporary importance of arches in real structures. Having established the importance of this neglected topic, the paper reports on strategies to insert the analysis of arch structures by modeling them use frame elements.

The first stage in this work was the identification of what topics about arches were covered in textbooks on structural analysis, at least those more commonly used in civil engineering courses in the USA. A list of books is given in the appendix, including the identification of the book  (title, authors, publishing house and year of publication), the coverage of arches (pages dedicated to arches, total number of pages, the ratio of arch pages to total number), and some comments about what special contents were covered (for example, only isostatic problems, only a definition of arch is given, the cover page of the book has an arch, etc.).

The total number of pages in each book excludes Appendix, Bibliography, Index. The pages dedicated to arches include pages in which arches are mentioned. A total of 21 books were examined. In 8 books there was no mention of arches, and in 4 other cases the number of pages was less than 1% of the total number in the book. In 6cases the pages of arches were between 1 and 2%. In 3 cases the book dedicated between 2 and 5% to arches, although mainly to isostatic arches.

The main conclusion is that arches are not covered in any detail in structural analysis books, for reasons that are not explained in the books.


Staad Information and Basic Tutorials

In the thirties last century, China imported electrostatic precipitator for the first time, times go to the sixties last century, Chinese began study the ESP; and came to seventies, Chinese had their own design of ESP basis on the mode. China imported several kinds the newest ESP technique again in eighties.

In the end of last century, they had almost all kinds of ESP, China became a really big country not only it’s own technique, but also the quantity of ESP which in use. In this significant progress process, the computer technology play a very important role, for example, Fluent used in CFD to model gas distribution, SCILAB using in emulation ESP, ATUTOCAD and PROE using in engineering drawing and three dimensions model,  STAAD and ANSYS integrate software in ESP design, all of  this gave a great push to the ESP technique improvement. 

STAAD is professional steel structure design software, it is very specific, and easy to use, it built-in several countries steel structure specifications, and was favorite by engineers. This article introduces the application of STAAD in ESP structure design

STAAD(Structural Analysis And Design)is a patent program which shared by Research Engineers International in California America. STAAD features a state-of-the-art user interface, visualization tools, powerful analysis and design engines with advanced finite element and dynamic analysis capabilities.

From model generation, analysis and design to visualization and result verification, STAAD is the professional’s choice for steel. Categorized load into specific load group types like dead, wind, live, seismic, snow, user-defined, etc.

Automatically generate load combinations based on standard loading codes such as ASCE, ACI, LRFD, BOCA, IBC, UBC, GB, etc. Automatic wind load generator for complex inclined surfaces, irregular panels and multiple levels also taking into consideration user-defined panels.

STAAD's User Interface is the industry standard. Complex models can be quickly and easily generated through powerful graphics, text and spreadsheet interfaces thatprovide true interactive model generation, editing, and analysis.

STAAD easily generates comprehensive custom reports for anagement, architects, owners, etc. The STAAD Structure Wizard contains a library of trusses and frames. Use the Structure Wizard to quickly generate models by specifying height, width, breadth and number of bays in each direction.

Reports contain only the information you want, where you want it. Add your own logo as well as graphical input and output results. Export all data to Microsoft Word or Microsoft Excel.

STAAD is a intelligent software for steel structure design, the main process is model generation, loading, analysis, criterion check, drawing, repeat design and optimize, then get the safety, reliable, reasonable and economy steel structure.

All the data of model and analysis storaged in a text file with suffix of .STD, this file can be changed by GUI or Editor. STAAD engine analysis STD, the result was storaged in the file suffix of like ANL, BMD, TMH, etc.


Hydrology Tutorials

The quality will be determined by the planned use. Physical, chemical, and bacteriological testing of source waters is required to determine the level of treatment to supply the necessary water quality.

When the quantity withdrawn exceeds the recharge rate, quality inherently decreases; therefore, this must be considered during design.

a. Physical characteristics. The physical characteristics of the raw water source that must be evaluated are total suspended solids (TSS) and temperature. Turbidity and silt density index (SDI).

(1) Total suspended solids. The total suspended solids level of raw water sources must be evaluated to determine the level of pretreatment processes required. Raw water having low total suspended solids levels generally requires less pretreatment. The source with the lowest total suspended solids is preferred.

(2) Temperature. The temperature of the raw water source must be matched to the specific desalination process. In extreme cases, the water temperature may control the desalination process selection. A climatological survey must be made prior to finalization of process selection to determine the seasonal maximum and minimum water temperatures of the proposed water sources.

(3) Turbidity and silt density index. These two characteristics provide two different measures of the amount of fine particulate matter in the water.

Turbidity is measured in nephelometric turbidity units (a measure of the amount of light scattered by a known water sample thickness). Silt density index is a measure of the amount of 0.45-micron filter plugging caused by passing a sample of water through the filter for 15 minutes.

Turbidity must be determined for all desalination processes. Also, the silt density index must be determined for water being considered for reverse osmosis treatment.

b. Chemical constituents. The chemical constituents of the raw water must be determined to provide information for treatment selection.

c. Bacteriological quality. The bacteriological testing of the raw water must include a type of a coliform indicator organism count.

Procedures for filter membrane, most probable number fermentation tube, and standard plate count, coliform organism bacteriological testing techniques can be found in Standard Methods for the Examination of Water and Wastewater and TB Med 576.

Manufacturers' recommendations as to the media and procedures used to identify microbiological activity detrimental to the operation of a particular desalination system shall be followed.


Bridge Design Tutorial

The structural detailer is responsible for the structural plan sheets. The plans shall be neat, correct, and easy to follow and drawn to scale. The structural detailer may also assist the designer and design checker in such areas as determining control dimensions and elevations, geometry, and calculating quantities.

Some detailing basics and principles:

a. Refer to BDM for detailing practices.

b. Provide necessary and adequate information. Try to avoid repetition of information.

c. Avoid placing too much information into any one sheet.

d. Plan sheets should detail in a consistent manner and follow accepted detailing practices.

e. Provide clear and separate detail of structural geometrics. Use clear detailing such as “stand alone” cross sections or a framing plan to define the structure.

f. Avoid reinforcing steel congestion.

g. Check reinforcement detail for consistency. Beware of common mistakes about placement of stirrups and ties (such as: stirrups too short, effect of skew neglected, epoxy coating not considered, etc.). Check splice location and detail, and welding locations.

h. Use cross references properly.

i. Use correct and consistent terminology. For example, the designation of Sections, Views, and Details.

j. Check for proper grammar and spelling.

k. On multiple bridge contracts, the structural detailing of all bridges within the contract shall be coordinated to maximize consistency of detailing from bridge to bridge. Extra effort will be required to assure uniformity of details, particularly if multiple design units and/or consultants are involved in preparing bridge plans. This is a critical element of good quality bridge plans.

l. Refer to the Bridge Book of Knowledge for current special features and details used on other projects.


Soil Mechanics Tutorials

Soil designations in this manual conform to the Unified Soil Classification per ASTM D2487, Classification of Soil for Engineering Purposes.

Classify soils in accordance with the Unified System and include appropriate group symbol in soil descriptions. A soil is placed in one of 15 categories or as a borderline material combining two of these categories. Laboratory tests may be required for positive identification.

a. Sands and Gravels.
Sands are divided from gravels on the No. 4 sieve size, and gravels from cobbles on the 3-inch size. The division between fine and medium sands is at the No. 40 sieve, and between medium and coarse sand at the No. 10 sieve.

b. Silts and Clays.
Fine-grained soils are classified according to plasticity characteristics determined in Atterberg limit tests.

c. Organic Soils.
Materials containing vegetable matter are characterized by relatively low specific gravity, high water content, high ignition loss, and high gas content. Decrease in liquid limit after oven-drying to a value less than three-quarters of the original liquid limit is a definite indication of an organic soil.

The Unified Soil Classification categorizes organic soils based on the plotted position on the A-line chart. However, this does not describe organic soils completely. For the characteristics of the Unified Soil Classification System pertinent to roads and airfields, see NAVFAC DM-5.4.

3. TYPICAL PROPERTIES. Some typical properties of soils should be based on laboratory and/or field testing, and engineering evaluation.


Soil Mechanics Tutorials

A complete engineering soil identification includes: (a) a classification of constituents, (b) the description of appearance and structural characteristics, and (c) the determination of compactness orconsistency in situ.

a. Field Identification. Identify constituent materials visually according to their grain size, and/or type of plasticity characteristics per ASTM Standard D2488, Description of Soils (Visual-Manual Procedure). (1) Coarse-Grained Soils. Coarse-grained soils are those soils where more than half of particles finer than 3-inch size can be distinguished by the naked eye.

The smallest particle that is large enough to be visible corresponds approximately to the size of the opening of No. 200 sieve used for laboratory identification. Complete identification includes grain size, color, and/or estimate of compactness.

(a) Color. Use color that best describes the sample. If there are two colors describe both colors. If there are more than two distinct colors, use multi-colored notation.

(b) Grain Size. Identify components and fractions in accordance Coarse-Grained Soils.

(c) Grading. Identify both well graded and poorly graded sizes as, under Supplementary Criteria for Visual Identification.

(d) Assigned Group Symbol. Use Table 3 for estimate of group symbols based on the Unified Classification System.

(e) Compactness. Estimate compactness in situ by measuring resistance to penetration of a selected penetrometer or sampling. If the standard penetration test is performed, determine the number of blows of a 140 pound hammer falling 30 inches required to drive a 2-inch OD, 1-3/8 inch ID split barrel sampler 1 foot.

The number of blows thus obtained is known as the standard penetration resistance, N. The split barrel is usually driven 18 inches. The penetration resistance is based on the last 12 inches.

1) Description Terms.
2) Compactness Based on Static Cone Penetration Resistance, q+c,. Reference 2, Cone Resistance as Measure of Sand Strength, by Mitchell and Lunne, provides guidance for estimating relative density with respect to the cone resistance.

 If q+c, and N values are measured during the field exploration, a q+c,-N correlation could be made, and is used to describe compactness. If N is not measured, but q+c, is measured, then use 7.1-N = q+c,/4 for sand and fine to medium gravel and N = q+c,/5 for sand.

(f) Describe, if possible, appearance and structure such as angularity, cementation, coatings, and hardness of particles.

(g) Examples of Sample Description: Medium dense, gray coarse to fine SAND, trace silt, trace fine gravel (SW). Dry, dense, light brown coarse to fine SAND, some silt (SM).


Soil Mechanics Tutorials

a. Principal Soil Deposits
Soil deposits grouped in terms of origin (e.g., residual, colluvial, etc.) and mode of occurrence (e.g., fluvial, lacustrine, etc.).

b. Importance.
 A geologic description assists in correlating experiences between several sites, and in a general sense, indicates the pattern of strata to be expected prior to making a field investigation (test borings, etc.).

Soils with similar origin and mode of occurrence are expected to have comparable if not similar engineering properties.

For quantitative foundation analysis, a geological description is inadequate and more specific classification is required.

A study of references on local geology should precede a major subsurface exploration program.

c. Soil Horizon.
Soil horizons are present in all sedimentary soils and transported soils subject to weathering. The A horizon contains the maximum amount of organic matter; the underlying B horizon contains clays, sesquioxides, and small amounts of organic matter.

The C horizon is partly weathered parent soil or rock and the D horizon is unaltered parent soil and rock.


How To Design Retaining Wall


Determine the factor of safety (FS) against sliding and overturning of the concrete retaining wall in Figure. The concrete weighs 150 lb/ft3 (23.56 kN/m3, the earth weighs 100 lb/ft3 (15.71 kN/m3), the coefficient of friction is 0.6, and the coefficient of active earth pressure is 0.333.

Calculation Procedure:

1. Compute the vertical loads on the wall

Select a 1-ft (304.8-mm) length of wall as typical of the entire structure. The horizontal pressure of the confined soil varies linearly with the depth and is represented by the triangle BGF in Fig. 10

Resolve the wall into the elements AECD and AEB; pass the vertical plane BF through the soil. Calculate the vertical loads, and locate their resultants with respect to the toe C. Thus:

W1 = 15(I)(ISO) = 2250 Ib (10,008N);
W2 = 0.5(15)(5)(150) = 5625;
W3 =0.5(15XS)(IOO) = 3750

Then ^W = 11,625 Ib (51,708 N). Also, Jc1 = 0.5 ft; X2= 1 + 0333(5) = 2.67 ft (0.81 m); Jc3 = 1 + 0.667(5)-433 ft (1.32m).

2. Compute the resultant horizontal soil thrust

Compute the resultant horizontal thrust T Ib of the soil by  applying the coefficient of active earth pressure.

Determine the location of T. Thus BG = 0.333(1S)(IOO) = 500 Ib/lin ft (7295 N/m); T = 0.5(15)(500) = 3750 Ib (16,680 N); y = 0.333(15) = 5 ft (1.5m).

3. Compute the maximum frictional force preventing sliding

The maximum frictional force Fm = where M = coefficient of friction. Or Fm = 0.6(11,625) - 6975 Ib (31,024.8N).

4. Determine the factor of safety against sliding 

The factor of safety against sliding is FSS = FJT = 6975/3750 = 1.86.

5. Compute the moment of the overturning and stabilizing forces

Taking moments with respect to C, we find the overturning moment = 3750(5)
= 18,750 lb-ft (25,406.3 N-m).

Likewise, the stabilizing moment = 2250(0.5) + 5625(2.67) + 3750(4.33) = 32,375 lb-ft (43,868.1 N-m).

6. Compute the factor of safety against overturning

The factor of safely against overturning is FSO = stabilizing moment, lb-ft (N-m)/overturning moment. lb-ft (N-m) = 32,375/18,750 = 1.73.

How to determine the size of elastomeric bearings?

Civil Engineering Tutorials

For elastomeric bearing, the vertical load is resisted by its compression while shear resistance of the bearing controls the horizontal movements.

The design of elastomeric bearings are based on striking a balance between the provision of sufficient stiffness to resist high compressive force and the flexibility to allow for translation and rotation movement.

The cross sectional area is normally determined by the allowable pressure on the bearing support.

Sometimes, the plan area of bearings is controlled by the maximum allowable compressive stress arising from the consideration of delamination of elastomer from steel plates.

In addition, the size of elastomeric bearings is also influenced by considering the separation between the structure and the edge of bearing which may occur in rotation because tensile stresses deriving from separation may cause delamination.

The thickness of bearings is designed based on the limitation of its horizontal stiffness and is controlled by movement requirements. The shear strain should be less than a certain limit to avoid the occurrence of rolling over and fatigue damage.

The vertical stiffness of bearings is obtained by inserting sufficient number of steel plates.

In bridge widening projects, the method of stitching is normally employed for connecting existing deck to the new deck. What are the problems associated with this method in terms of shrinkage of concrete?

Civil Engineering Tutorials

In the method of stitching, it is a normal practice to construct the widening part of the bridge at first and let it stay undisturbed for several months. After that, concreting will then be carried out for the stitch between the existing deck and the new deck.

In this way, the dead load of the widened part of bridge is supported by itself and loads arising from the newly constructed deck will not be transferred to the existing deck which is not designed to take up these extra loads.

One of the main concerns is the effect of stress induced by shrinkage of newly widened part of the bridge on the existing bridge.

To address this problem, the widened part of the bridge is constructed a period of time (say 6-9 months) prior to stitching to the existing bridge so that shrinkage of the new bridge will take place within this period and the effect of shrinkage stress exerted on the new bridge is minimized.

Traffic vibration on the existing bridge causes adverse effect to the freshly placed stitches. To solve this problem, rapid hardening cement is used for the stitching concrete so as to shorten the time of setting of concrete.

Moreover, the stitching work is designed to be carried out at nights of least traffic (Saturday night) and the existing bridge may even be closed for several hours (e.g. 6 hours) to let the stitching works to left undisturbed.

Sometimes, longitudinal joints are used in connecting new bridge segments to existing bridges. The main problem associated with this design is the safety concern of vehicles.

The change of frictional coefficients of bridge deck and longitudinal joints when vehicles change traffic lanes is very dangerous to the vehicles. Moreover, maintenance of longitudinal joints in bridges is quite difficult.

Note: Stitching refers to formation of a segment of bridge deck between an existing bridge and a new bridge.

What is the function of longitudinal joints in concrete road pavements?

Civil Engineering Tutorials

A longitudinal joint consists of a tie bar placed at the mid-depth of a concrete pavement and it is not intended for joint lateral movement.

Then one may doubt the reasons of placing longitudinal joints in concrete pavements. In fact, longitudinal joints are normally designed at a regular spacing e.g. 4.5m to accommodate the effect of differential settlement
of pavement foundation.

When uneven settlement occurs, the tie bars in longitudinal joints perform as hinges (Ministry of Transport (1955)) which allow for the settlement of concrete carriageway.

Moreover, it also serves to cater for the effect of warping of concrete due to moisture and temperature gradients by permission of a small amount of angular movement to occur so that stresses induced by restrained warping can be avoided.

Dowel bars are provided in longitudinal joints for the following reasons:

(i) In case of the occurrence of uneven settlement between adjacent panels, it helps to maintain a level surface by transfer of loads through dowel bars.

(ii) Keep the longitudinal joints close.

Why are concrete profile barriers designed with curved surface profiles?

Civil Engineering Tutorials

Safety fencings are designed to contain vehicles in the carriageway in which they are traveling and prevent them from rebounding into the road and causing hazards.

For normal fencing design, when vehicles crash into safety fencings, it will give way so as to absorb as much energy as possible, thus reducing the impact forces on the vehicles.

Moreover, it serves to realign the vehicles along the carriageway when vehicles hit on them. However, for concrete profile barriers they are not designed to absorb energy during vehicle crashing, but to hold the vehicles hitting on them.

In this connection, concrete profile barriers are designed with curved profiles so that vehicles can mount and go up partly on them, and yet they will not cause overturning of vehicles. Reference is made to Arthur Wignall, Peter S. Kendrick and Roy Ancil.

For shallow-angle crashing of cars, they would climb on the lower slope face of concrete profile barriers. On the other hand, when a car hits at a large angle to the barrier, the bumper collides with the upper sloping face of concrete profile barrier and the car rides upwards.

This provides the uplift of the car whose wheels move up the lower sloping face of the barrier. It is not intended to lift the car too high, otherwise it may result in rolling. Since the friction between the wheels and barriers provide extra lifting forces, it is undesirable to design rough finish on these faces.

In essence, the kinetic energy of the car during collision is transformed to potential energy during its lifting up on profile barrier and finally converted back to kinetic energy when the car returns to the road.

Note: For details of concrete profile barriers, reference is made to HyD Standard Drawing No. H2101A.

What are different approaches for reclamation in deep water region and shallow water region?

Civil Engineering Tutorials

To illustrate the different approaches adopted for reclamation in deep water and shallow water region, the following example is used:

In deepwater region, consider the seabed level is –8.5mPD. After laying of geotextiles and 1.5m thick sand blanket, the top level of sand blanket is about –7mPD. Split barges are deployed for dumping public fill to –2.5mPD.

Afterwards, end dipping of public fill by trucks will be carried out up to +2.5mPD which is the designed reclamation level. Between level –2.5mPD and +2.5mPD, it is too shallow for split barges to enter the water, thus the method of end dipping is used instead.

For shallow water region, the seabed level is taken as –5.5mPD in this example. With the laying of geotextiles and 1.5m sand blanket into position, the top level of sand blanket is about –4mPD.

In this case, split barges are also used for reclamation work between the level –4mPD and –2.5mPD. After that, if end dipping is used for reclamation work above –2.5mPD, then in considering the relative thin layer of fill above seabed (1.5m sand blanket + 1.5m sand blanket), it stands a high chance that mud wave would occur in seabed.

Therefore, half-loaded derrick barges are employed for reclamation up to level 0mPD. With a thicker layer of public fill now, end dipping can then be used for reclamation between 0mPD and +2.5mPD.

This above reclamation sequence is just an example to demonstrate the different considerations for reclamation in deep water and shallow water region.

What are the components of a waterproofing system in the roof of a typical pumping station?

Civil Engineering Tutorials

In the design of a waterproofing system at the roof of a pumping station, normally the following components are:

(i) Above the structural finish level of the concrete roof, a screed of uniform thickness is applied to provide a smooth surface for the application of waterproofing membrane. (Screed of varying thickness can also be designed on the roof to create a slope for drainage.)

The screed used for providing a surface for membrane should be thin and possess good adhesion to the substrate. Moreover, the screed aids in the thermal insulation of the roof.

(ii) Above the screed, waterproofing membrane is provided to ensure watertightness of the roof.

(iii) An insulation board may be placed on top of waterproof membrane for thermal insulation. In cold weather condition where the loss of heat at the roof is significant, the insulation board helps to reduce these losses.

On the contrary, in summer the roof is heated up by direct sunlight and the insulation layer reduces the temperature rise inside the pumping station.

What is the function of shear keys in the design of retaining walls?

Civil Engineering Tutorials

In determining the external stability of retaining walls, failure modes like bearing failure, sliding and overturning are normally considered in design. In considering the criterion of sliding, the sliding resistance of retaining walls is derived from the base friction between the wall base and the foundation soils.

To increase the sliding resistance of retaining walls, other than providing a large self-weight or a large retained soil mass, shear keys are to be installed at the wall base. The principle of shear keys is as follows:

The main purpose of installation of shear keys is to increase the extra passive resistance developed by the height of shear keys.

However, active pressure developed by shear keys also increases simultaneously. The success of shear keys lies in the fact that the increase of passive pressure exceeds the increase in active pressure, resulting in a net improvement of sliding resistance.

On the other hand, friction between the wall base and the foundation soils is normally about a fraction of the angle of internal resistance (i.e. about 0.8 ) where is the angle of internal friction of foundation soil. When a shear key is installed at the base of the retaining wall, the failure surface is changed from the wall base/soil horizontal plane to a plane within foundation soil.

Therefore, the friction angle mobilized in this case is instead of 0.8 in the previous case and the sliding resistance can be enhanced.


All About Civil Engineering

Civil engineering involves the planning, designing laying out and constructing of buildings, railroads, highways, bridges, tunnels. They also work closely with architects and environmental engineers. 

Since civil engineering is very broad, civil engineering jobs are dependant on each chosen specialisation taken by the engineer at University. However for these specialisations there are usually three functions that are performed by the civil engineer. The planning( includes feasibility studies and designs), pre development(actually working on site making sure safety and all procedures are being followed correctly) and post development.

About the middle of 18th century when more attention was paid towards the building and roads and bridges etc, for civil purpose only, a new class of engineers developed who began to be called "civil engineers".

The institution of engineering in its charter in 1828 as the act of directing the great souses of power in nature for the use and convenience of man, as the means of production and of traffic in state, both for external and internal trade. 

This definition covered almost all the branches of engineering which have now developed separate entity. In early 19th century due to the growing emphasis on specialization numerous groups and sub-divisions of engineering like mechanical, mining and electrical engineering etc, came into being. With the growth of these branches of engineering the scope of civil engineering has been restricted.

Civil engineering now concerns only with the design and construction of roads, railways, bridges, canals, docks, ports, harbours, lighthouses, drainage works and break water

Civil engineering includes the planning, designing, construction, and maintenance of structures and altering geography to suit human needs. Some of the numerous subdivisions are transportation (e.g., railroad facilities and highways); hydraulics (e.g., river control, irrigation, swamp draining, water supply, and sewage disposal); and structures (e.g., buildings, bridges, and tunnels).
Civil Engineering fields also includes the following specialisations:
•  Structural engineering 
•  Geotechnical engineering 
•  Environmental engineering 
•  Transportation engineering

And other fields as:
Construction engineering
Earthquake engineering
Environmental engineering
Geotechnical engineering
Water resources engineering
Materials engineering
Structural engineering
Transportation engineering

Tune in to this blog for more post and tutorials about Civil Engineering.


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