Sunday, 15 April 2012

4th-yr-Abcm-Cinema balcony structural details

Question: Cinema balcony 8m deep and 18 m wide in steel is proposed for cinema hall. Assume suitable data draw the following:
a). part key plan and section scale 1:100 showing structural components of the balcony.
b). cross section of the balcony (in large scale) showing arrangement of structural components and false ceiling details, etc.

Answer:  Since cinema balcony space will not allow columns on cantilevered side, we can place steel H sections in U form.  So on 8m depth side we will place 3 columns at 4m centre to centre or 4 columns at 2.66m centre to centre (preferred). The sizes of columns will vary slightly depending on span. On 18 m side we can go for 3m centre to centre. These columns will come only on one side leaving the other side columns free for un-obstructed viewing. 

The steel columns can be H sections or built-up sections or combined together can be used. 

H - sections are popularly known as the rolled steel joists or beams. It consists of two flanges connected by a web. It is designated by overall depth, width of flange and weight per meter length. They are available in various sizes varying from 75mm x 50 mm at 59.84 N to 600 mm x 210 at 976.1 N.

Some more sizes of H sections are given below: 
150 mm x 100 mm at 166.77 N
150 mm x 150 mm at 265.85 N
300 mm x 150 mm at 369.84 N
450 mm x 250 mm at 907.43 N
600 mm x 250 mm at 1423.43 N

The R. S. joists are economical in material and they are suitable for floor beams, lintels, columns, etc. The economy in material is achieved by concentrating the material in two flanges where the bending stresses are maximum. 


In order to make steel beams and columns of suitable strength and rigidity, the standard sections are built-up or combined together. It is thus possible for a designer in the steel structures to make use of available standard sections of structural steel and prepare a built-up section as per requirements. 
Some combinations for your information:

a). One I section with two plates at top and other at bottom. (plates sizes vary from 5 mm to 50 mm with corresponding weights per meter square are 384.55 N and 3850.43 N respectively).
b). Two I sections and two plates one at top and other at bottom (if design requires two plates at top and bottom can also be used).
c). 3 I sections with i) at end of flange of one I section you can place center of web of two I sections one each on either side mirrored. ii) on both sides of vertical web you can place one each I section on either side with flange abutting web mirrored. 
d). I section in center and two channel sections on either side. 
e). Two channel sections with some gap between two mirrored C sections with two plates on either side. 
f). A combined I section built by placing two plates with some gap with four angles placed mirrored and two plates on top and bottom one each. 

For our problem at hand we can choose option b). with two I sections of 300 mm x 150 mm at 369.84 N and plate 10 mm at 769.82 N two nos at top and bottom of width 450 mm. 

or alternatively we can choose single I section of 450 mm x 250 mm at 907.43 N (I am no expert in steel designs but this is my best educated guess). 

please note we will have perimeter main beams on all three sides of balcony of I sections of 450 mm x 250 mm at 907.43 N or alternative you can use castellated beam 250 mm x 600 mm. 

(Castellated beams refer to the type of beams which involve expanding a standard rolled steel section in such a way that a predetermined pattern is cut on section webs and the rolled section is cut into two halves. The two halves are joined together by welding and the high points of the web pattern are connected together to form a castellated beam. The castellated beams were commonly used in Europe in 1950s due to the limited ranges of the available steel rolled section and the cheap labour cost. In terms of structural performance, the operation of splitting and expanding the rolled steel sections helps to increase the section modulus of the beams. Moreover, it is versatile for its high strength to weight ratio so that lighter section can be designed with subsequent cost saving in foundation).

Along the depth of 8 m balcony side near the screen you can give lattice girder beam approximately 2.2 meter deep made of mirrored C channels and angles of 75 x 50 x 6 mm welded together with gusset plate of 6mm thick. 

please note that the cross section across the width of 8 m deep may have slope of necessary angle to get clear viewing angles. this is approximately 30 cm at every 1.2 m depth of balcony. You can safely take two meter slope in 8 meter deep balcony. 


The various members of a steel framed structure are to be suitably connected for transfer of loads. Following are the methods adopted for connecting the members of steel work:

i). Bolts: When it is desired to have temporary connections, the bolts, nuts and washers are used. The bolts may be adopted also if rivets are difficult to use.

ii). Rivets: These are made from the round rods of mild steel and consist of a hemispherical bottom-shaped head with a cylindrical shank. The holes are drilled in the members to be connected. The rivet is heated red hot and is inserted in the hole. The second head is formed on the other end of shank by pneumatic hammer or otherwise. This process make an effective joint and this joint can fail only on the failure or destruction of the rivet. 

iii). Welding: The process of welding is most popular nowadays. It is carried out either by oxy-acetylene gas or electric arc. The welding rods provide the molten metal necessary to fill the joint. There are various types of the welded joints. However, the lap, butt and fillet joints are very common. By careful design of the welded joints, it is possible to make the joint of same strength as that of solid member. 

please note that while connecting all steel joists if necessary angle cleats, gusset plates, etc may be used of adequate size and weight to transfer the loads. 


Please take precaution of encasing the R.S.J. by concrete so as to prevent rusting of R.S.J. The use of steel sections makes the floors light and economical. 

On top of these beams we can make filler joists floors: In this type of floors, the small sections of rolled steel joists are placed in concrete. The joists (sizes 101.6 mm x  101.6 mm  at 127.48 N) rested on steel beams at c/c distance of 600 mm to 900 mm. The joists also act as a reinforcement. The concrete should completely surround the rolled steel joists and beams with minimum cover of 25 mm over the filler joints.  

Over these floors light weight concrete is poured to get steps to get proper viewing in balcony for cinema viewing. The false ceiling will be as per acoustics design requirement which will be suspended by fixing necessary hooks in concrete in gypsum board finish. 

Or alternatively you can hollow core precast slab fixed by angle cleat over the castellated beam. Again light weight concrete can be poured to form visual angle for clear viewing. 

I hope that cinema balcony in RCC is relatively easy and can be solved by you all. As general thumb rule for every feet of span between columns give one inch depth of beam. With this calculations you can do approximate design of RCC beams. 

Please note that you are not required to write all the above details in your answer. Please fill in details of your answer proportionate to marks and time available. Try to attempt all questions briefly before you start filling in more details. 

i regret that i could not manage to draw the sketch as required to explain above details but in case of any doubts please send comment on blog or message on my mobile 8692077376.

atule kedia.


4th-yr-Abcm-Contiguous Piled, Secant Piled & Diaphragm Basement Walls.

The use of contiguous / secant piling and diaphragm wall construction techniques to construct retaining walls is common in large commercial basement projects. The nature of these construction techniques is such that the only practical option is to apply waterproofing systems to the internal face of the retaining wall.

Any excavation done to go down in basement and if the extent of basement is up to plot limit, then the soil or earth need to be stopped, retained or shored by diaphragm wall, shoring, secant or sheet piling or other methods.

Selection of type of retaining wall:
Selection of retaining wall type and support system are usually made on the basis of:
a)   Foundation of adjoin properties and services
b)   Designed limits on wall and retained ground movements
c)   Subsoil conditions and ground water level
d)   Working space requirements and site constraints
e)   Cost and time of construction
f)    Flexibility of the layout of the permanent works
g)   Local experience and available construction plant
h)   Maintenance of the wall and support system in permanent condition

The commonly used retaining walls to support excavations are as follows:
a)   Sheet pile wall (vertical members
    of interlocking profiled steel plate driven into the ground to support the    sides of a major excavation - also called trench sheeting).
b)   Soldier pile wall (soldier piles (steel H sections @ 3m c/c) and horizontal wood logging)
c)   Continuous bored piles wall (these are all primary piles with reinforcement in each and placed next to each other)
d)   Secant piles wall (primary piles and secondary piles slightly overlap each other with reinforcement in alternative pile)
e)   Diaphragm wall (mostly is rcc precast wall 1.2 m to 1.5 m wide with end to end interlocking joints, but sometimes also cast in-situ)

Diaphragm wall is commonly used as permanent wall system. Diaphragm wall offers most water tightness compared to other wall systems. Similar to continuous bored piles wall secant piles wall, diaphragm wall also causes minimum noise and vibration disturbance. However it is not suitable for highly collapsible soil during trenching.
Secant pile wall.... see below...

Saturday, 14 April 2012

4th-yr-Abcm-ribbed slab with hollow pre-cast concrete blocks...

for more information on ribbed slab with hollow pre-cast concrete check following ppt.

as usual please focus on fundamental issues in ppt and ignore structural calculations, etc...

later in day i will up load more things on water proofing of basement...

atule kedia

4th-yr-Abcm-How To Build A "Room-Within-A-Room" (sound proof room)

Get the ultimate in sound-proofing by borrowing this idea used in professional recording studios.
One of the most effective ways to control the leakage of sound is to build a room within a room. Forcing the sound waves to have to travel through a double-wall, or a double-floor weakens it considerably. This also has the double effect of isolating the movie-goers within the room from sounds coming in from the outside.

Lets say you have an existing room in your basement thats already framed and drywalled. To build your room within a room, you'd have to construct four new walls, a new ceiling, and a new floor. There has to be absolutely no contact between the inner and outside walls and ceiling. The whole thing would then have to "float" above the existing cement floor on special rubber footings.
You would start by building a floor using similar techniques used to frame a wall. To reduce the amount of wasted space, the width and length of the new floor should be about 6 inches less than the width and length of the room it will be in. This will provide enough of a gap between the rooms to reduce the transmission of sound.
Instead of using drywall, you would use 3/4" plywood on the bottom of the new floor. You'd then fill the gaps between the studs with fiberglass insulation. You can also use special insulation products such as Owens Corning QuietZone and Roxul's Safe'n Sound which provide both fire resistance and sound deadening. Be sure to use a breathing mask and gloves when handling any fiberglass insulation product. Before finishing the floor with 3/4" plywood, mark off the location of each stud. These marks will help you easily find the studs later when you have to screw the walls to them.

Build the new floor on 1/4" to 1/2" thick rubber isolation mats. These mats are designed to virtually eliminate the transmission of sound vibrations. They're usually a specialty item but can easily be purchased online.
Now that our room within a room has its new floor, its time to build the walls. You will frame each wall and hang drywall on the side that will be facing the gap. Raise each wall into position and screw them into the floor's studs using the markings you made earlier.
Regular ceilings in a house are built using ceiling joists. These are wooden members that span the width of a room and hold up the ceiling, roof, or floor of a house. In our case, we can get away with using 2x4's for our ceiling joists since we don't need to hold up anything other than the ceiling's drywall and some light fixtures. Its pretty hard to frame a completed ceiling and lift it into place so you'll have to build it piece by piece.
A wall has both a top plate and a bottom plate. Ceilings on the other hand have header joists to which the 2x4's are connected. Install a pair of header joists on two walls that oppose each other. Starting at one end of the room, screw a series of 2x4's between the header joists 16 inches on center.
When each wall and ceiling are framed and installed, its time to lay out your electrical wiring. Though this site is for the do-it-yourselfer, I recommend you hire a professional electrician for this part of the project. With the electrical wiring completed and inspected, its time to install more sound insulating fiberglass insulation between the wall studs and in the ceiling.
You'll then finish the job by filling in the empty space between the exposed studs in the walls and ceiling with more fiberglass insulation. When done, you'd hang the rest of the drywall on the inside walls of your new room. You can rent a panel lift or use a T-brace to help lift the drywall to the ceiling. You can use a solid wood or steel door and you can install weather stripping to seal off any cracks.
With all this talk about insulation, you'd be right if you started to think our new room would get pretty warm. I didn't talk about ventilation just yet. I'll reserve that for another blog.

4th-yr-Abcm-Acoustic Windows

Manufacturing of sound proof glass having two glasses with air vacuum between both the glasses provide adequate vision of the production process windows can be incorporated into the design. This is custom made window in factory in controlled environment to create air vacuum. The design of windows, particularly large window areas, requires great care in the details of glass responses. any size can be manufactured.

Popular Solutions for:
  • Factory offices
  • Factory enclosures
  • TV studios
  • Audiometric rooms
  • Test cells
  • Translation booths
  • Music practice rooms
  • Hotels
  • Offices
Acoustic Windows is also known as ,Soundproof Windows, Noise Proof Windows, Vacuum Glass, Sound Proof Glass, Sound Proof Glass Window, Sound Transmission Class, Sound Transmission Coefficient
Acoustic Performance
Noise Reduction of 30-60dB(A)

Friday, 13 April 2012

4th-yr-Abcm-Dia grid-flat slab-waffle-slab

Dia grid beam floor in R.C.C.: in this system there will be diagonal beams across the slabs when seen in elevations but none in horizontal direction. This system gives more space in centre of building because there are no columns. Also due to lack of horizontal beams it gives neat space within.To find out more about dia grid, please put the following on your web browser:

Definition of Diagrid

1.    a structure of crossing support beams [n -S]

Waffle slab details:

Presentation on Reinforcing Detailing Of R.C.C Members

Flat slab details:

R.C.C. Floors: 

Flat slab:  An important development in RCC floor is that of a flat slab RCC floor. In this method slab is built monolithically, with supporting columns only without provision for beams. The flat slab may either be with drop or without drop. The term drop is used to indicate that part of slab around the column having greater thickness than the rest of the slab.  See the sketch above to give various nomenclature of flat slab.
The reinforcement in the flat slab can be arranged either in two – way system or four – way system. For ordinary loading conditions, the two-way system of reinforcement is generally adopted. The flat slab construction grants the following advantages.
i). as the slab is constructed without any beam, a flat ceiling is obtained which gives attractive appearance and greater height without obstructions for services. 
ii). It is considered less vulnerable in case of fire as compared to the ordinary slab-beam construction.
iii). The concrete is more logically used in this type of construction and hence it proves to be economical for large spans with heavy live loads.
iv). The formwork is simple and economical.
v). The plain ceiling grants better diffusion of light.

Hollow block and rib floors: In this type of floors, the hollow blocks of clay or concrete are used to reduce the total weight of the floor.
In one form, the blocks are placed 100 mm apart and in this space, the mild steel bars are placed as shown in sketch. A minimum cover of 80 mm is kept at the top . suitable flooring at top and ceiling finish are provided. The blocks are provided with rough or grooved surface so that they can develop enough bond with concrete. This type of floor is economical, fire-proof, sound-proof and light in weight. If properly designed, this type of floor can even be used to carry heavy loads. The plumbing and electrical installations can be conveniently carried through the hollow blocks without affecting the appearance. As hollow blocks replace a portion of solid concrete, the dead weight is reduced and thereby the economy is achieved. These floors are widely used for buildings like hospitals, hotels, schools, offices, etc. the structural hollow clay floor tiles should be free from cracks and they should be of uniform color and texture. It is desirable to keep projections on one of the extreme face of such tiles so as to facilitate the application of plaster. The weight per meter length of structural hollow clay floor tiles does not exceed 140 N. The length, width and height of structural tiles are from 450 mm or 900 mm, 190 mm or 240mm and 70 mm or 90 mm respectively.

Pre-cast concrete floors: With the development of pre-cast concrete construction technique, it is possible to prepare the pre-cast units for the floor. These pre-cast units are available in suitable sizes as can be conveniently handled, transported and fixed. They may be supported either on walls or on rolled steel joists. The sides of each unit contain grooves which are used to connect the adjacent units.

Advantages of pre-cast concrete floors: Following are the advantages of the pre-cast concrete floors:
i). The construction work can be carried out speedily as there is absence of operations like watering, curing, etc.
ii). The members are light in weight and hence the foundation cost proves to be economical.
iii). They are fire – proof and  sound – proof.
iv). They do not require formwork during construction.
v). They have good thermal insulation.
Disadvantages of pre-cast concrete floors: Following are the disadvantages of the pre-cast concrete floors:
i). There are chances for breakages to occur during their transport from factory to the site of work.
ii). They prove to be economical and cheap only when manufactured on a large scale.
iii). They require careful supervision and skilled labor during their manufacturing process.
iv). They require fairly uniform spacing of beams and columns throughout the structure which becomes practically difficult.
v). They should be properly designed to resist the stresses developed during transport and handling operations.

please follow my post and put your queries in comments. it is very simple procedure. click 'follow' on left hand top side and fill in details as requested. i will try my best to give answers.

atule kedia....