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The analysis and design of structures to resist the effect produced by time dependent forces or motions requires conceptual idealizations and simplifying assumptions through which the physical system is represented by an idealized system known as the analytical or mathematical model. These idealizations or simplifying assumptions may be classified in the following groups;
Material assumptions
Loading assumptions
Geometric assumptions

Structrual Dynamics Theory and Computation

Title of the Book

Structural Dynamics
Theory and Computation

Fifth Edition
Updated with SAP2000

Authors of the Book

Mario Paz
Speed Scientific School
University of Louisville
Louisille, KY
William Leigh
University of Central Florida
Orlando, FL.

Contents of the Book

Part 1 Structures Modeled as a Single-Degree-of-Freedom System
Part 2 Structures Modeled As Shear Buildings
Part III Framed Structures Modeled As Discrete Multi-Degree-of-Freedom Systems
Part IV Structures Modeled with distributed properties
Part V Special Topics: Fourier Analysis, Evaluation of Absolute Damping, Generalized coordinates
Part VI Random Vibration
Part VII EarthQuake Engineering

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Concept of Reinforced Earth

Reinforcement in the form of steel or synthetic strips called geo-strips are placed within an embankment, containing soil in various layers compacted mechanically; the granular material of embankment is linked by means of friction. The embankment becomes a self supporting structure, such a structure is called reinforced earth structure.

Earth Reinforced with Geo-strips and Reinforced Earth Panels

Concept

Construction of reinforced earth is a very simple process. The principle concept of reinforced earth is similar to that of a reinforced concrete that contains steel, aggregates and fines. In reinforcing earth process we reinforce the earth by means of steel or synthetic geo-strips.

Stresses that are generated within the embankment is transferred and resisted by these reinforcing strips. 

Concept of Reinforced Earth Works (REW)

History

Constructions using these techniques are known to have existed in the 5th and 4th millenniums B.C. Since early civilizations, man has attempted to use soil with other materials to enable it for being used for his necessities. Typical early use includes us of branches of tree etc. to support tracks over marshy areas and to build hutments. Structures are also built by insects and birds using mud and leaves.  These are all familiar sights even today. This kind of principle is also used in building parts of Great Wall of China and the Babylonian Ziggurats i.e. temples.

Great Wall of China

In the 19th Century Passel used tree branches to reinforce back fills in order to reduce the earth pressure and thereby economize the retaining walls. 

Textile material was perhaps first used in road construction in south Carolina in the early 1930s. The first use of a woven synthetic fabrics for erosion control was made in 1958 by Barrett.

Construction

Reinforced earth system consists of following items;

a) Facing or the skin of the embankment
b) Reinforcing geo-synthetic strips
c) Soil in lifts or layers

During the construction phase we first do a lean within the boundary of embankment upon which the reinforced earth panels or skin of the reinforcement is placed. In this boundary of panels we place the selected material containing fines and gravels in lifts or layers. Each lift is mechanically stabilized by using a roller. We in this case don’t use sheep foot roller or vibratory roller, we use simple steel drum roller to do the compaction as well as ensuring stability of the structure.

The skin or reinforced earth panels have a path or passage for geo-synthetic strips which is called connectors mostly they are in C shape so they are called C-Connectors.

A bridge Abutment

These strips after passing through C-Connector is jointed with a reinforced steel bars placed at center in a specified distance. With each lift the process repeats and as a result we get a well compacted reinforced earth embankment. Water sealant foam is applied between each panels to ensure it as a water tight structure.

Advantages

Following are some of few positivity in Reinforced Earth Works

Reinforced Earth Panels Facing

a) Easy Placement

Construction is repetitive and simple, panels, strips, granular fill and then compaction

b) Positive Connection

Galvanized reinforcing strips are connected to concrete panels with structural bolts

c)    Engineered Backfill

Alternating layer of reinforcing strips and backfill are applied and compacted.

d)   Structural Facing

TerraClass facing panels are easily handled by placement crew.

What is slab?

Structural Concrete Slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs, bridges, and other types of structures. The slab may be supported by walls, by reinforced concrete beams usually cast monolithically with the slab, by structural steel beams, by columns, or by the ground. The depth of a slab is usually very small compared to its span.

What is a slab? Or Slab System?

Firstly we should not confuse this word with SLAB which is acronym of Slow Low and Bangin which is mainly used in the south for any car that is fully customized.
Concrete slab is a common structural element of modern building. That is usually horizontal and has smaller thickness comparative of its span.

Slabs are used to furnish a flat and useful surface in reinforced concrete construction.

Classification or Type of Concrete Slab

In general, slabs are classified as being one-way or two-way. Slabs that primarily deflect in one direction are referred to as one-way slabs. When slabs are supported by columns arranged generally in rows so that the slabs can deflect in two directions they are usually referred to as two-way slabs.

One way and two way slabs

One more definition regarding one-way and two –way slab is that if one direction span to other direction span ratio (or more precisely if longer dimension to shorter dimension ratio) is greater than 2 it is termed as two way slab, otherwise if less than two it is termed as two-way slab.

One way slab with beams

two-way slab with beams

Classification of Two way Slabs

Two way slabs may be strengthened by the addition of beams between the columns, by thickening the slabs around the columns (drop Panels), and by flaring the columns under the slabs (Column Capitals).

Flat Plates Slab Definition 

These are solid concrete slabs of uniform depths that transfer loads directly to the supporting columns without the aid of beams or capitals or drop panels.

flat plate

Flat Slabs Definition 

Flat slabs include two-way reinforced concrete slabs with capitals, drop panels, or both. These slabs are very satisfactory for heavy loads and long spans. Although the formwork is more expensive than for flat plates, flat slabs will require less concrete and reinforcing than would be required for flat plates with the same loads and spans. They are particularly economical for warehouses, parking and industrial buildings, and similar structures where exposed drop panels or capitals are acceptable.

Flat Slab

Flat slabs Vs Flat Plate Slabs

• Flat plate slabs can be constructed quickly due to their simple form work and reinforcing bar arrangements. 
• They need the smallest overall story heights to provide specified headroom requirements, and they give the most flexibility in the arrangement of columns and partitions. 
• They also provide little obstruction to light and have high fire resistance because there are few sharp corners where spalling of concrete might occur. 
• Flat plates are probably the most commonly used slab system today for multistory reinforced concrete hotels, motels, apartment houses, hospitals, and dormitories. 
• Flat plat slabs present a possible problem in transferring the shear at the perimeter of the columns. In other words, there is a danger that the columns may punch through the slabs. 
• As a result it is frequently necessary to increase column sizes or slab thickness or to use shear heads. Shearheads consist of steel I or channel shapes placed in the slab over the columns. 
• Although such procedures may seem expensive, it is noted that the simple formwork required for flat plates will usually result in such economical construction that the extra costs required for shearheads are more than canceled. For heavy industrial loads or long spans, however, some other type of floor system may b required. 

Beam supported slab Definition

A two-way slab with beams is a type of floor system is obviously used where its cost is less than the costs of flat plates or flat slabs. In other words, when the loads or spans or both become quite large, the slab thickness and column sizes required for flat plates or flat slabs are of such magnitude that it is more economical to use two-way slabs with beams, despite the higher form work costs.

Complete Design of Cantilever Retaining Wall [pdf]

Cantilever Retaining wall is a reinforced cement concrete (RCC) Structure that is used to retain and hold back loose soil and gravel behind where there are abrupt changes in slope beyond their natural and stable angle of repose.

Complete Design of Cantilever Retaining Wall

Design Criteria

As far as the stability of a retaining wall is concerned; it is of two types (i) external stability and (ii) Internal Stability

in external stability we try to make cantilever wall resist the overturning, sliding and settlement while in internal stability we try to make it resist the shear and bending moment. Usually in cantilever retaining wall only flexural and temperature or shrinkage reinforcement is provided and shear reinforcement is not provided as it would cause steel congestion, thus when there is requirement of shear reinforcement the area of concrete is increased.

In this post i will be sharing with you a pdf document containing the complete design example of a cantilever retaining wall. 

Steps

The usual steps involved are as follows;

(i) Determination of preliminary dimensions of cantilever wall
(ii) checking external stability
(a) F.O.S against overturning
(b) F.O.S against soil pressure or settlement
(c) F.O.S against sliding and determining whether key is needed or not

(iii) Design of Heel Cantilever for shear and flexural
(iv) Design of Toe Slab for shear and flexural
(v) Reinforcement of Stem
(vi) Determining the cut length for reinforcement in stem by the help of graph
(vii) Checking the ACI conditions
(viii) Temperature and Shrinkage reinforcement
(ix) Final Presenting the results

Document

Download Complete Design of Cantilever Retaining wall

Disclaimer 

This design example is only for educational usage, the consequences of its usage for any commercial or educational work will be the responsibility of the user and iamcivilengineer.com is by no means responsible for it. 

From Editor's Desk

Its been a long time we havn't post any useful data, but this design example will surely break that break. I hope you would like it we need your feedback and your response. Share it with your friends as well. 

Retaining Walls, the support soil needs to stand up

We know that soil or any other loose granular material has a safe angle of repose at which the soil or material can withstand without any requirement of confinement or support. But due to practical and property restrictions we in some cases need to cut or fill the soil at some unstable angle which if unsupported might cause failure of the slope.

Concrete Retaining Wall

If we provide stable slope rather than steep slope; we might need more space there and sometimes more economy is required; to cater this problem we use the retaining wall to support the material laterally after justifying its usage from economic considerations.
Thus we can define retaining wall;

What is Retaining Wall?

As a structure or a part of structure that holds back and retained the loose material behind within a limited space to provide safety and economy one at the same end.

 Or
McCormac and Nelson defines it as;

Retaining wall is a structure built for the purpose of holding back or retaining or providing one-sided lateral confinement of soil or other loose material.

Aurther H. Nilson and others define the retaining wall as;

Retaining walls are used to hold back masses of earth or other loose material where conditions make it impossible to let those masses assume their natural slopes.

Example Of Retaining Wall

Typical example of the retaining wall might be that of highways; in highways we have restricted property space called the right-of-way and within that limited space we have to provide the required width of the highway by using the cut and fill soil, and there those steep slopes come which needs retaining wall to get that support;

Types of Retaining Walls

Most commonly five types of retaining walls are used named as under;
(a)    Gravity Retaining wall
(b)    Cantilever Retaining Wall
(c)    Counter-fort Retaining wall
(d)    Buttress Retaining wall
(e)    Bridge-abutment type retaining wall

Gravity Retaining Wall;

The Gravity Retaining wall as the name suggests provide support or restraint to the loose material laterally because of its self-weight, it generally doesn’t contain reinforcement and mostly is used for 10 ft height and no more than that because more height will increase the need of more thicker cross-section and ultimately it will not be economical.

Gravity Type Retaining Wall

Cantilever Retaining Wall

Is a reinforced retaining wall that acts like a cantilever beam, it has four parts, the portion of the base slab or footing below the retained material is heel, and the other portion is toe, the vertical wall is called stem and to increase the slide friction key is provided below the base slab or footing.
The weight of the retained soil on the top of heel provides additional stability to the structure. It is mostly used for relatively greater heights upto 10 to 20 ft. 

Cantilever Type Retaining Wall

Counter-fort Retaining Wall

In Counter-fort retaining wall the stem and heel (the portion of the base slab below the retained slow) are joined together by inclined transverse walls at intervals called counterforts, Counterforts are in tension and mostly called counterfort ties. Counterfort retaining wall is mostly used for higher heights up to 25ft or more.

Counter Fort Retaining Wall

Buttress Retaining Wall

Buttress retaining wall is similar to counterfort retaining wall except that the inclined transverse walls are provided at the front of the stem called buttresses and acts like a compression member. Because of this property they are more stable and more economical, but because the buttresses are visible and occupies the space un-necessarily that might be useful if buttresses were not there; thus they are not generally used;

Buttress Retaining Wall

 Bridge Abutment Retaining Wall

It is a wall types bridge abutment, abutment and piers are the column-type structures used to support the deck of the bridge, the first and the last support of the bridge are called abutments because they retains the soil where as other supports are called piers. This type of retaining wall is just a simple cantilever retaining wall except that the bridge deck provides an additional horizontal restraint at the top of the stem. This wall is thus designed as a beam with fixed support at the bottom and simply supported or partially restrained at the top. 

Bridge Abutment Retaining Wall

From Editor’s Desk

Retaining Walls are very sensitive type of structures that protects our infrastructure like highways and roads from land-slides etc and helps us to let the roads be clear for us. In the retaining wall drain pipes are also provided along with pot-holes for reducing the amount of lateral load and to allow the wall to remain stable against overturning and sliding.
Hope you like this post, don’t forget to share it with your friends and colleagues.
Happy Civil Engineering!
 

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Download Design of Reinforced Concrete by Jack C. McCormac and James K. Nelson

Reinforced Concrete Structures are widely being constructed throughout the world and because of availability of raw materials required to design a mix, they lead other building materials like wood, stones etc. Mostly the code and guidelines used to design reinforced concrete structures is that of American Concrete Institute (ACI). In this post I will be sharing with you a book Titled “Design of Reinforced Concrete ACI 318-05 Code Edition”.  The material of the book is written in such a manner as to interest students in the subject of Reinforced Cement Concrete and to encourage them to continue its study in the years to come. This book is used in many institutions as a text book for the three-credit course.

For this book there is a special website being built for the students and instructors, i.e. www.wiley.com/college/mccormac The website contains solution manuals, figures, tables, design aids etc.

The main feature of this book is the computer examples and problems, which utilizes computer programs like excel etc to solve many problems. The book comprises of 21 chapters with extension of appendixes as A, B and C and a glossary is provided at the end.

Chapter Details

The chapter details are as follows;
Chapter 1 deals with introduction to the design of Reinforced cement concrete, Chapter 2 is about flexural analysis of beams, Chapter 3 is about strength analysis of beams according to ACI code. Chapter 4 is about Design of Rectangular Beams and one-way slabs, Chapter 5 is about Analysis and Design of T Beams and Doubly Reinforced Beams, Chapter 7 is about Bond, Development Lengths, and Splices, Chapter 8 is about Shear and Diagonal Tension, Chapter 9 is about Introduction to Columns, Chapter 10 is about Design of Short Columns Subjected to Axial Load and Bending, Chapter 11 is about Slender Columns, Chapter 12 is about Footings, Chapter 13 is about Retaining Walls, Chapter 14 is about Continuous Reinforced Concrete Structures, Chapter 15 is about torsion, Chapter 16 is about Two way slab Direct Design Method, Chapter 17 is about Two way Slabs, Equivalent Frame Method, Chapter 18 is about Walls, Chapter 19 is about Prestressed Concrete, Chapter 20 is about FormWork and Chapter 21 is about Reinforced Concrete Building Systems.
Special Design procedure for Strut and Tie approach for deep and dapped end beam is given at the appendix C.

Book Title

Design of Reinforced Concrete ACI 318-05 Code Edition

Author(s)

Jack C. McCormac of Clemson University

James K. Nelson of Western Michigan Univeristy

 Publisher

John Wiley & Sons.

Download Link

Download Design of Reinforced Concrete By Jack C. McCormac and James K. Nelson

Keywords for This book

Download Design of Concrete book, Download Design of Reinforced Concrete By Jack C. McCormac, Download Reinforced Concrete 7th Edition, Download Book for concrete structures, Download Pdf Reinforced Concrete by McCormac
 

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10+ Important Points for Civil Site Engineers to Remember:

Site Engineers Play an important role for the success or failure of any project; they are the front force of any construction or consultant company, they have to face harsh weathers, large amount of man power; and they comes in direct execution of any project; to know more about site engineers, what are its responsibilities; what are the skills required; move to this post;

Site Engineer, skills, salary, education required

Following are few general points to remember for civil site engineers to make the construction work easier while maintaining the quality of construction.

Site Engineer Important Points to remember: Dreamstime.com

1. Lapping is not allowed for the bars having diameters more than 36 mm.
2. Chair Spacing Maximum spacing is 1.00 m (or) 1 No per 1m²
3. For Dowels rod minimum of 12 mm diameter should be used.
4. Chairs minimum of 12 mm diameter bars to be used.
5. Longitudinal reinforcement not less than 0.8% and more than 6% of gross C/S.
6. Minimum bars of square column is 4 No’s and 6 No’s for circular column.
7. Main bars in the slabs shall not be less than 8 mm (HYSD) or 10 mm (Plain Bars) and the distributors not less than 8 mm and not more than 1/8 of slab thickness.
8. Minimum thickness of slab is 125 mm.
9. Dimension tolerance for cubes + 2 mm.
10. Free fall of concrete is allowed maximum to 1.50 m.
11. Lap slice not to be used for bar larger than 36 mm.
12. Water absorption of bricks should not be more than 15 %.
13. PH value of water should not be less than 6.
14. Compressive strength of Bricks is 3.5 N/mm²
15. In steel reinforcement binding wire required is 8 kg per MT.
16. In soil filling as per IS code, 3 samples should be taken for core cutting test for every  100 m².

Concrete testing by Ultrasonic Pulse Velocity (UPV)

How many times as a civil engineer, you have to test a concrete? Hunh! So many Times! But most of the time you find concrete cubes and cylinders being crushed by Compression Testing Machine (CTM) in the laboratory. Now that broken cylinder or cube is useless for you, although you can recycle it but even then a recycled material can never meet the standard of first class material. Think about hundreds of cubes and hundreds of cylinders being tested, broken and then the crew throw them away.

Performing UPV test by direct method

And then the Non-destructive Testing (NTD) comes to rescue;

“Non Destructive Testing are non invasive techniques to determine the integrity of a material, component or structure or quantitavely measure some characteristic of an object”

Non-destructive Testing is an easy way to detect or inspect the defects on the surface of the concrete or structure, It is a fast techniques and need not any sort of huge calculation or waiting, Mostly this technique is used in specialist high risk areas such as nuclear and Sea shore structures, gas and oil pipelines.

There are a lot of method involved in non-destructive testing like rebound test, ultrasonic pulse velocity test; Here we are focusing on Ultrasonic Pulse Velocity Test (UPV)

We know that velocity of ultrasonic waves is directly proportional to the density or in other words the modulus of elasticity of the material; and as far as the concrete is concerned we have a direct empirical relations between Modulus of Elasticity of Concrete (E) and compressive strength of the concrete (fc’). Thus if we can measure the velocity of ultrasonic waves through concrete we might easily get the compressive strength of the concrete.

Idea of Receiver and Transmitter 

Methods of testing:

There are three methods of testing the concrete depending upon the placement of the transducers;

Direct Method:

If the two transducers are placed in such a way that one is placed at one end and other at the other end throughout the member it is direct method

Indirect method

In this method both transducers are place on the same surface of concrete and the receiver receives the pulse coming after striking the concrete molecules

Semi-direct method

It is mostly used for corners of concrete members

Methods of UPV tests

Apparatus Required:

Electrical Pulse Generator – Transducer – Amplifier Electronic Timing Device

Designation:

ASTM C597 - 09

How it is performed?

By using the calibration cylinder, first of all the calibration of the instrument was check, the default ultrasonic pulse velocity through the calibration cylinder was 57.8 micro seconds.

After calibration testing, on the two surface of the concrete some sort of vasline or any similar material is applied so that the two transducers might be leveled;

The travel time of velocity is read from instrument in microseconds; this travel time is converted to velocity by using the relation s=vt; or v=s/t; if we are testing two different ends of cylinder; the distance between transducer will be 1 feet thus velocity will be 1/t where t is converted to seconds from microseconds;

This velocity in ft/sec is then related to fc’ by using a graph between pulse velocity (ft/sec) on x-axis and fc’ (psi) on y-axis

Graph Between Pulse Velocity and Fc'

To compare the results between destructive compression testing of cylinder with this non-destructive compression testing; the cylinder is then tested with compression testing machine.

At the end the percentage difference between two fc’s is reported.

Discussion

The curves between fc’ and ft/sec velocity is different for dry concrete and we concrete; the reason being if the concrete is dry the voids will be filled with air; velocity of pulse through air being lesser then that in water the pulse velocity reading will be smaller in case of dry material then that of wet material.

The transducers must not touch the reinforcement bars in the concrete; as the assumption of this method is that the material must be homogeneous, isotropic and elastic;  

Determining the Quality of Concrete Grading by using pulse velocity

Above 4.5 km/sec                            Excellent

3.5 to 4.5 km/sec                              Good

3.0 to 3.5 km/sec                              Medium

Below 3.0                                            Doubtful

performing UPV test indirectly

Advantages and Disadvantages of the Ultrasonic Pulse Velocity Test:

As far as the advantage of the ultrasonic pulse velocity is concerned; it has high penetrating power which ensure very easy measurement even for the very deep concrete members; it is highly sensitive thus giving accurate results; easy to use for estimating the size, shape and nature of flaws in the concrete member;

But this method also have some limitations like; manual operation of the instrument requires careful attention by experienced technicians; if the surface is irregular it is difficult to estimate accurately the pulse velocity; test objects must be water resistant.