Expert: Bruce E. Johnson - 9/14/2008

Question
QUESTION: Hi Bruce,
     Hoping that you are fine. My questions are that
why starters are given prior to concreting in columns.
Trusses that span over great lengths have camber..how
camber is given in trusses.
how to check the quality of sand on a construction site??

Best Regards





ANSWER: Hi Mkahzumi, maybe it is a localized terminology but I am not familiar with the term "starters" in reference to columns.  If the column is steel and sits on a concrete footing it is normally attached to that footing with bolts that have been embedded into the footing concrete.  Then the base plate of the column sits on nuts that are used to level and plumb the column.  Following this the column is then grouted into place to assure that it will not settle or move.

As far a camber in trusses.  This is a gradual high point generally in the middle of a truss so that once it is set and gravity begins to pull down on the middle of the truss the upward camber will allow that truss to better resist those gravitational forces.  The camber is determined during the engineering of the truss and is based on the deflection of material over time.

Looking at sand on a jobsite depends on what it is used for.  Sand for mortar must be clean and free of impurities.  A simple test is to put a cup full of the sand into a glass jar and some clean water.  Shake the jar up and let it sit.  If the water becomes cloudy or murky then the sand has impurities in it and depending on how dirty it is will determine if it to be used for structural purposes.  Generally speaking when sand is delivered to a jobsite it will come with a desination, mason sand, playground sand, stucco sand,fill sand etc.  Mason sand may be a bit coarser than stucco sand.  Playground sand is too fine to be used for structural purposes.  Fill sand will have impurities in it such as silt and clay this gives it a cohesive quality and allows it to be compacted properly.  It should not have any grass or wood or other organic materials in it as they will leave a void in the sand when they decay.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson  bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Hi man,
 Thanks for the other detailed answers. Starters are used for concrete columns. When the columns are to be poured above plinth beam, starters are given. Starters are rectangles of size equal to that of column and having thickness 1.5 in max. They are made by cement and sand mix of 1:2

Regards


Answer
Hi again Makhzumi, So when you are referring to starters you refer to the grout (cement mixture) that fills in the void between the bottom of the column and the plinth or footing after the column is set and leveled.  Thanks for that.  I've never heard that particular specific term.  When looking at a structural steel plan or structural plan, the point in discussion has always been designated as "grout column base".  We accomplish this pouring non shrink, non metallic grout into a slightly oversized form that surrounds the column base. The grout fills up the void between the base plate and the bearing concrete. Also regarding your previous question for sand quality: I rely on an engineering testing agency to test all my concretes, sands and fills.  We test fill for consistency based on a proctor of the material and compared with ensuing deliveries or changes in pit locations.  Just thought I'd let you know.   Sincerely bruce e johnson..bejohnsonconsulting.com