Engineering Updates

SPT Value Correction – The observed SPT values as measured in the field are not reliable due to multiple factors and therefore need  to be corrected. Two types of corrections which are usually applied for this task are: dilatancy and overburden pressure corrections. Dilatancy correction –    The dilatancy correction can only be applied when the test is conducted in fine or silty saturated sand when recorded blow count is greater than 15. The correction factor as suggested by Terzaghi and Peck (1967) is as follows. Where, N o  = Observed N-Value N c ‘ = Corrected N – Value In no case, the corrected values shall be greater than twice the observed values. Overburden correction –  With the increase in confining pressure in sands N-Values are increased considerably. As a result values of relative density other than actual values are obtained and therefore, the observed values are to be corrected. The N-Values at shallow depths are under-estimated and at ...

HOW TO CALCULATE BEARING CAPACITY OF SHALLOW FOUNDATION IN SAND FROM SPT VALUES OR N-VALUES  (IS-6403) STEP-1 Perform standard penetration test  on the location for which you want to calculate bearing capacity. This is done as per standard procedure given in IS-2131. Standard penetration test must be done at every 75 cm in vertical direction. STEP-2 Decide the depth, width and length of foundation for initial calculation. This is a trial and error process. In the first attempt, you can never get the exact size of foundation which will satisfy all of your needs. STEP-3 Apply necessary  corrections to the standard penetration test values . Calculate the cumulative average value of corrected SPT values from the base level of foundation to a depth equal to 2 times the width of foundation. STEP-4 Correlate the above cumulative average SPT value with the fig given below to find out the corresponding angle of shearing resistance (ϕ). Relation between ph...

According to the Concrete Reinforcing Steel Institute (CRSI), “form work and its associated labor is the largest single cost segment of the concrete structural frame—generally more than 50%.”           • maintaining constant depth of horizontal construction           • maintaining constant spacing of beams and joists           • maintaining constant column dimensions from floor to floor           • maintaining constant story heights Standard Forms Since most projects do not have the budget to accommodate custom forms, basing the design on readily available standard form sizes is essential to achieve economical form work. Also, designing for actual dimensions of standard nominal lumber will significantly cut costs. A simplified approach to form work carpentry means less sawing, less piecing together, less waste, and less time. this results in reduced labor and mated costs and fewer op...

Things that are discussed and attended during the concept design stage: • T ype of construction — reinforced concrete, precast concrete, reinforced masonry, structural steel, cold formed steel, wood, etc. • Column locations — A uniform grid facilitates repetitive member sizes, reducing the cost and increasing the speed of construction. Bay dimensions may also be optimized to minimize material quantities while efficiently accommodating specific space requirements, such as parking garages and partition layouts. • Bracing or shear wall locations — Horizontal forces due to wind, earthquakes, etc. must be transferred down from the superstructure to the foundations. The most efficient means of accomplishing this is usually to provide vertical bracing or shear walls oriented in each principle direction, which must be coordinated with functional and aesthetic requirements for partitions, doors, and windows. • Floor and roof penetrations — Special framing is often required to accom...

Steel + Concrete = Safe Steel only = Expensive Concrete only = Are you mad? Everyone knows that concrete is damn good in compression while steel is great in tension. Steel is also good in compression but because it has very high strength, the cross section generally becomes small and the smaller the cross section the more are the chances of buckling, while concrete on the other hand has low strength so we require larger cross sections and in doing so we overcome the buckling effects. Now, the important question is why only steel? Why not aluminium? The reason is, when both the material are heated they possess a similar coefficient of thermal expansion, concrete has of the order of 14 x 10^-6 while steel has 12.6 x 10^-6. So when it gets hot, both the material experience almost similar strains and there is no internal stress formation. Now one more question comes to mind is, what would happen even if internal stresses are formed? Well, those small strains can create tensile stresses in...