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Friday, March 31, 2017

Top 3 Planning and management software of civil engineering





  1. Microsoft Project
  2. Primavera
  3. Project Kickstart

how to check The Dead load as per Staad for no of floors

1. Self weight (columns,beams and shear walls for the entire building)
2. Brickwall over the exterior beams except on shear wall only are added.
3. The dead load on slab- Self weight of slab+Finish+Construction load +15% for furniture, staircase, water tank etc is added with an intensity of 6KN/Sq.m.
A manual check for these items are carried out as:
  • Dead load: Area of floor x no. of floors x intensity of load
  • Brickwall load:




    Total length of beam in one floor =
    Load per floor =
    Load due to brickwall alround exterior beams =
    Load due to Parapet 1.0 m height of 4.5” wall=
    Total dead load due to brickwall =
  • SELF WEIGHT OF:
    • COLUMNS =
    • Beams for all floors
    • Shear wall:

Thursday, March 30, 2017

HOW TO DO MANUAL CHECK AGAINST STAAD RESULTS FOR SEISMIC FORCES?

Example
The structure is 36x21m and is symmetrical in x and Z direction as well as in vertical elevation and its total height from the footing is 74m.(21 storey)
The building is in Zone III and the time period as per IS 1893-2002(PartI) for infill is taken 0.09h/√d.
After analysis through STAADPRO the followings check is carried out to verify and check the results between manual calculation and the software results.




-------------------------------------------------------------------------------------------------

A. TIME PERIOD:

As per IS CODE 1893-2002(Part I) T =0.09h/ √d where d is the direction along the EQ forces.
Tx =0.09x74/ √36 =1.11 Sec.
Tz =0.09h/ √21 =1.453 Sec.
The output of STAADPRO is
TIME PERIOD FOR X 1893 LOADING = 1.11000 SEC
TIME PERIOD FOR Z 1893 LOADING = 1.45333 SEC
******************************************************************************************

Manual checking of Staadpro output

LOADS:

Correct assessment of loads both dead and live loads are important since excessive assumed loads may lead to uneconomical member sizes and footing sizes. Also excessive loads will be adding more weight in the case of seismic forces.
In order to have equilibrium i.e .╬úV=0 under the Load case DEAD LOAD calculate the total dead load on all floor slabs and check it against the output by the program.

METHOD TO CHECK:





Using a single support for the whole structure RUN the ANALYSIS and find out the total support reaction in Y axis i.e FY from the output of the program. Check whether the above two values are in agreement to the manually calculated values. If the results vary then there is some error or mistake took place while entering the input.
The same procedure can be carried out for the LIVE LOAD for both FLOOR LIVE LOAD and ROOF LIVE LOAD cases also.
If the single support is not considered or modeled then use all the supports and copy the values of Fy to EXCEL and get the sum of the FY and check whether it tallies with the manually calculated values.

WIND LOAD:

To find the point load FX or FZ at a joint as nodal wind force calculate the tributary area for the corresponding node and multiply it with the intensity of loading.
For example:
Area = (h1+h2)/2*(L1+L2)/2* intensity of loading.
Please note that the consistence unit shall be used.
Where h1 and h2 are the height above and below the joint in meters and L1 and L2 are the width of the bay on either side of the node in meter units.
If      h1 =4.0m
and h2=3.0m,
         L1=5.0m
and L2=6.0m
then the tributary area for the node is
=(4+3)/2*(5+6)/2 = 19.25sq.m.
Using an intensity of 1KN/sq.m the nodal force shall be =19.25 KN.
This can be verified with the values generated by the program.

SUPPORT CONDITIONS:

Usually while modeling a structure either FIXED or HINGED support condition is proposed. If the support condition is FIXED the there shall be six restraints i.s. FX,FY ,FZ, Mx, My and Mz
For HINGED there shall be no moments. In order to account for the soil spring the modulus of subgrade reaction Ks has to be considered for the support condition.
Ref:  by T.Rangarajan

Manual checking of Staadpro inputs

Model checking





It is important to check the UNITS at every stage while modeling since it may lead to a unexpected error in the output. While modeling use of length units may be in meter for beam, column and plate and while entering the properties it is usual practice to make use of either mms or inch unit . While inputting the LOADS on members check the UNIT system is in KN and meter system since the program continues to use the previous unit till it is changed.
Before inputting the LOADS to the structure facility is available in STAADPRO as per the screen shot.
  • Check Multiple Structures.

Some times by mistake the user would have without his knowledge created too many members and structure. Better use this tool menu to remove the multiple structures. It is the responsibility of the applicator to verify that there exists only one structure and not more than it for any model.
Check for multiple structure in Staadpro
Check for multiple structure in Staadpro

Wednesday, March 29, 2017

Which type of multiple-cell box girder is better, cells connected by top flanges or cells connected both by top and bottom flanges?

When the depth of a box girder bridge exceeds 1/6 or 1/5 of the bridge width, it is recommended to be designed as a single cell box girder bridge. However, if the bridge depth is smaller than 1/6 of the bridge width, then a twin-cell or multiple cell is a better choice. However, even for wider bridges with small depths, the number of cells should be minimized
because there is not much improvement in transverse load distribution when the number of cells of box girder is increased to three or more. For multiple-cell box girders, there are generally two arrangements. The first one is that independent cells are connected by their top flanges only while the other one is that the cells are connected both at the top and bottom flanges. From the structural point of view, it is recommended to adopt the second arrangement. For the case of cells connected by top flanges only, their flanges are heavily stressed in the transverse direction owing to flexure which cannot be effectively distributed across the cross section.




boxgirder

Ref: Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Tuesday, March 28, 2017

How to see Reinforcement details in Staad.pro?





After you run analysis you can either see in output or postprocessing.
  • First method

As shown in figure below to see output u have to click on icon

staad2
OUTPUT FILE OF STAADPRO
You will see concrete design option on left click on that

reinforcement.jpg
BEAM REINFORCEMENT RESULT IN STAADPRO
You can see reinforcement on right side.
  • Second method

or you can see in postprocessing also. Run analysis , go to postprocessing. Than click on beam or column whose reinforcement you want to see. small window will open. Click on concrete design there you can see reinforcement.

3.jpg
BEAM REINFORCEMENT IN POSTPROCESSING IN STAADPRO

Thursday, March 23, 2017

What is sucker deck principle for variable depth bridge decks?

For a variable depth bridge deck, the depth of continuous multi-span bridge deck is increased in pier supports and this absorbs sagging moments in the mid-span with the consequent increase in hogging moments in pier supports.




Member Incidence command in Staadpro

Example of Member incidence command

1 1 3; 2 3 4; 3 4 2;
Above line indicates member number(1) , starting node (1), and ending node number (3).
member number(2) , starting node (3), and ending node number (4)
member number(3) , starting node (4), and ending node number (2)
separated by single spaces.

What are the advantages of piers constructed monolithically with the bridge deck over usage of bearings?




Basically, piers constructed monolithically with the bridge deck are advantageous in the following ways:
  1. In this way, it saves the construction cost of bearings by using monolithic construction between bridge deck and piers. Moreover, it is not necessary to spend extra effort to design for drainage details and access for bearing replacement. On the other hand, in maintenance aspect substantial cost and time savings could be obtained by using monolithic construction instead of using bearings as bridge.
  2. Monolithic construction possesses the shortest effective Euler buckling length for piers because they are fixed supports at the interface between bridge deck and piers.
Note: Monolithic construction means that piers are connected to bridge decks without any
joints and bearings.
Ref: Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Saturday, March 18, 2017

For the loading pattern to obtain maximum positive moment in a span of a continuous beam, why should alternative spans on each side of the span be loaded?




To acquire a maximum sagging moment in a span of a continuous beam, the general rule is to load the span under consideration and alternative spans on each side of the span. To account for this rule, let’s consider the following example. For instance, loads are applied to the mid-span of a multiple-span continuous beam. It is noticed that this loads induce positive moments near mid-span in all even spans. Therefore, if all even spans are loaded simultaneously, this will result in the increase of positive moments in all other loaded spans. Similarly, to obtain maximum negative moment at a support, load adjacent spans of the support and then alternative spans on each side.




What are the potential advantages of continuous multiple-span deck over simply supported multiple-span deck?





Movement joints are normally added to bridge structures to accommodate movements due to dimensional changes arising from temperature variation, shrinkage, creep and effect of prestress. However, the provision of excessive movement joints should be avoided in design because movement joints always encounter problems giving rise to trouble in normal operation and this increases the cost of maintenance. Some designers may prefer to add more movement joints to guard against possible occurrence of differential settlements. However, the effect of continuity is disabled by this excessive introduction of movement joints. 




From structural point of view, the use of continuous deck enhances the reduction of bridge deck thickness. Moreover, deck continuity allows the potential increase in headroom in the mid-span of bridges by using sucker deck principle.
Some designers may prefer to employ the use of simply supported multiple-span deck to guard against possible occurrence of differential settlements. However, the effect of continuity is undermined by the introduction of movement joints. In essence, the structural reserve provided by a continuous bridge is destroyed by the multiple-span statically determinate structure resulting from the addition of joints. Moreover, the reduction of joints in bridge structures represents substantial cost savings arising from the construction and maintenance costs of movement joints. The reduction of deck thickness helps to cut the cost for both the deck and foundation. In particular, the number of bearings in each piers is substantially reduced when compared with the case of simply supported multiple-span deck.

Ref: A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

What are the main potential benefits in using the bridge form of precast prestressed beams supporting in-situ concrete top slab?




The potential benefits of using the bridge form of precast prestressed beams supporting in-situ concrete top slab are:

(i) For bridges built on top of rivers and carriageway, this bridge form provides the working platform by the precast beams so that erection of falsework is not required.
(ii) This bridge form generally does not require any transverse beams or diaphragms (except at the location of bridge supports), leading to reduction of construction time and cost.
(iii) It creates the potential for simultaneous construction with several spans.
Ref: A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.




Friday, March 17, 2017

What is stress corrosion of prestressing steel?

Stress corrosion is the crystalline cracking of metals under tensile stresses in the presence of corrosive agents. The conditions for stress corrosion to occur are that the steel is subjected to tensile stresses arising from external loading or internally induced stress (e.g. prestressing). Moreover, the presence of corrosive agents is essential to trigger stress corrosion. One of the main features of stress corrosion is that the material fractures without any damage observed from the outside. Hence, stress corrosion occurs without any obvious warning signs.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Thursday, March 02, 2017

What are smart motorways?

What are smart motorways and how do they work?

SMART MOTORWAY TECHNOLOGY





Smart motorway technology is deployed to actively manage traffic flows and optimise the motorway network. 

Why do we need Smart Motorways?





The key aim of Smart Motorways is to reduce congestion and improve journey times by better managing the traffic using roadside technology infrastructure, associated control centres, systems and operational regimes.

Other benefits of differing types of Smart Motorway operational regimes have included reductions in accidents and reduced impacts on the environment associated with emissions from stationary or slow moving vehicles.

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