Questions and Answers

11/02/04

Some questions on certain KCE Specifications--

Section 2151     Excavation, Sheeting, Shoring, Underpinning, and Dewatering

1.2B     What is unclassified excavation?

            No extra $, rock or not

1.2F      What is a 3” minimum concrete work mat?

            To stop rock from fluffing up overnight

1.3O     What are inclinometer casings?

            Device we shove monitor down into to check for ground moisture

1.3P     What is a work slab?

            See 1.2F

2.1A     What does plasticity measure in soil?

            Flow, if liquid

2.3A     What is dywidag threaded bar?

            1-¼” diameter high strength bar

2.3A     Need general explanation regarding footing tie downs.

            To stop building from falling over

3.1A     Need general definitions of sheeting shoring, underpinning, bracing and sheet piling.

            See 3.1.F

3.1B     How is movement detection generally accomplished?

See 1.3O & sheeting & shoring, but generally it is detected with bar graph & reflector targets placed on soldier beam and read by instrument.

3.1F      Need general definition of rakers, tiebacks and walers.

            Rakers are diagonal steel members, kicked back into excavation to hold up waler soldier beams (removed); Tiebacks are drilled rods under adjacent property to hold up walers, horizontal members which hold up soldier beams – stressed and left in place; Soldier beams are vertical steel members, in this case drilled into ground and abandoned; Lagging is 3” / 4” boards between soldier beams

3.7B     Why do you need to chlorinate your wells once a month?

            To keep filters clean

Section 3300     Poured in Place Concrete

1.3B4   What is visqueen vapor barrier?

            Plastic sheet

1.3B9   What are the concrete additives hydrocide or pozzilith?

            Water-tightness

1.3B11  What is inertia or house keep slabs?

            Stops vibration from being felt in office space due to vibration

1.3B12  What is admixture?

            Additive to concrete mix

1.3B13  What are galvanized dove tail slots at masonry and galvanized reglets at flashing?

            To hold water-tightness elements into concrete

1.3B14  What are boxes for holes in concrete?

            M.E.P. (plywood, removed)

1.3B16  What is a concrete garage interceptor?

            Takes garage water & takes out contaminent

1.3B24  What is crystalline waterproofing?

            Hard finish, troweled on waterproofing

1.3B25  What is RXPlus floor/foundation walls and intersections?

            Black caulk for water finish

1.3B29  What is lean concrete?

            2000 psi (little cement)

1.3B38  What is lagging at perimeter of building?

            See 3.1F above.

1.3D7   What are corner guards for the parking garage?

            Angles to stop cars from damaging concrete

1.6        That’s a lot of test.  How are we organizing all that information?

            The tests described are required to ensure proper quality control on the job, and to meet all Code and Arlington County requirements:

            1.6       TESTS

            A.         Concrete: The Contractor shall name his source of supply for concrete materials, and shall submit to the Structural Engineer for approval, copies of the mix designs he proposes to use, certified and sealed by a Professional Structural Engineer registered in the Commonwealth of Virginia . A recognized testing laboratory, approved by the Structural Engineer, shall be engaged to perform the following services: (Expense of this work shall be borne by the Owner.)

                        1.         Test cement in accordance with the ASTM physical test requirements. One test shall be made for each carload of cement.

                        2.         Make Quality Test of materials including reinforcing steel, but Certified mill test reports will be acceptable.

                        3.         Concrete test cylinders shall be taken, cured and tested in accordance with the ASTM Specifications.  Concrete cylinders shall be paid for by the Owner.  Each cylinder shall be clearly marked to permit easy identification. Sets of test cylinders shall be taken and tested as follows:

                                    a.         It shall be the responsibility of the Concrete Subcontractor to notify the testing laboratory of the concrete pouring schedule with a minimum of 24 hours notice in order that the sample cylinders may be taken. Provide minimum of 24 hours notice to testing laboratory.

                                    b.         Take a set of cylinders for each 100 cubic yards of concrete for each day's pour and for each class of concrete.  These cylinders shall be made at the point of discharge from the truck and shall be made in accordance with the latest edition of ASTM C_172 and shall be laboratory cured and tested in accordance with the latest edition of ASTM C_31 and ASTM C_39.  The cylinders shall be made and tested in accordance with the following schedule:

                                                (1)        Columns (with f'c # 5000 psi), walls, beams, framed slabs:  Each set shall consist of eight (8) cylinders, 2 field cured and 2 lab cured cylinders to be tested at 7 days, and 2 field cured and 2 lab cured cylinders to be tested at 28 days.

                                                (2)        Footings, slabs on grade:  Each set shall consist of four (4) cylinders, 2 lab cured cylinders to be tested at 7 days, and 2 lab cured cylinders to be tests at 28 days.

                                                (3)        Columns / slabs with f'c $ 5000 psi:  Each set shall consist of twelve (12) cylinders, 2 field cured and 2 lab cured cylinders to be tested at 7 days, and 2 field cured and 2 lab cured cylinders to be tested at 28 days, plus 2 lab cured cylinders to be tested at 84 days and 2 lab cured cylinders to be tested at 112 days.

                                    c.         Additional tests as directed by the Architect's Structural Engineer.

                                    d.         Take additional cylinders as required for stripping decisions; cost to be born by the Contractor.

                        4.         Submit test reports, within 7 days of the test,  as follows:

                                    a.         One each directly to the Architect, Owner's Representative, governmental officials and the Structural Engineer.

                                    b.         If the test cylinders indicate that the concrete does not meet the requirements of the project, the Structural Engineer may require additional testing to be done.  The expense of the additional tests, in any case, shall be borne by the Contractor.

2.1I      What are water stops?

            See 1.3B25

3.1        Concrete Proportions, Strengths, and Mixes

B1        What are concrete slumps?

Amount concrete slumps … once test cone in which concrete is place is removed – this helps measure water content of concrete

3.1D     Why do you recommend all concrete being machine mixed?

            Because there is no room for batch plant on site

3.1I      What is retempering of concrete?

            Fucking with it after truck shows up

3.3               Forms, Shoring and Tolerance

C          What do you mean every unstressed floor shall be reshored by two fully stressed floors?

            So it won’t collapse

3.4               Reinforcing Steel

D         What are temperature bars?

            Bars place where there are no bars in one-way slabs to control cracking

F          What are high chairs, beam bolsters, and stirrups?

High chairs hold up top reinforcing; beam bolsters hold up beam reinforcing, and stirrups are part of shear design

3.5               Placing Concrete

G          What do you mean additional concrete shall be in each bay on metal deck equal to the beam camber amount?

            So no extra $ is charged when formwork deflects, and more than “neat” volume is poured, until concrete hardens

Section 3315     Post Tensioning

1.2A     What is full tendon bonded post tensioning?

            Grout pumped into cable tendons are in & make anchorage bond continuous

1.3D     What is bursting steel?

            Steel at trumpets @ ends to stop concrete from blowing up

1.3E     What are additional cylinders?

            Additional test 6”x12” cylinders

1.3F      What are grouting tendons?

            See 1.2A above

1.8               Shop Drawings

C          What are jack clearances, stressing sequence, initial tensioning forces, gauge pressers, and tendon elongation?

            Braided wires ± 1/” diameter are rolled out in plastic sheets on formwork help up by slab bolster and high chairs and placed with a parabolic type profile to specified dimenions we design.  At the ends of beams the wires flare out in both directions to cover essentially the whole end of the beam in a pepper box fashion.  These are dead end enclosed on the street side and steel trumpet and wedges on the stressing end.  Once the concrete reaches a certain strength, before the formwork is removed, the tendons are pulled by hydraulic jack, one at a time, until a predetermined lengthening is gained (elongation based on wire strength and force we want in cable.  The wedges are driven into place, and the tails of the wires left hanging out.  Elongation is observed by our inspector and reported to our office.  Once we review and assure ourselves we have the force we want, and we have the concrete breaks to verify the concrete strength we want, we write burn off letter and stripping letter allowing the tendon tails to be burned off and the slabs stripped.  Once burned off there is no real way to get more force in member.

D         What is a friction wobble coefficient?

            Depends on trumpet and sheathing dimensions

2.1               Materials

B4        What are oil tempered wires?

            Rubbed with oil for corrosion protection

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11/03/04

More Questions & Answers, on a variety of topics:

1Q.      Curing the design phase, how is a structure itself determined (steel vs. concrete)?  Eliminating the fact that concrete is good for hotels for painted ceilings and the fact that concrete is good for downtown D.C. buildings due to the overall height requirement, what else dictates steel vs. concrete?

1A.      Structural steel vs. concrete is usually based on:  spans, building height, foundation considerations, lead time (foundation hole or not), load carrying capacity, future use considerations, access restrictions.

2Q.      Why do so many projects follow this same pattern:  Something appears wrong with the concrete mix.  Lots of repetitive failures on multiple cores.  We call a big meeting.  Testing agency blames the concrete supplier, supplier blames the agency.  Owner yells at structural.  Miraculously, the  problem is solved and far fewer sub-standard breaks follow.  Here is the bottom line, if it is so easy to get the “mix” right, why not simply do it right  from the start?

2A.      The issue is money.  Owners don’t want to spend a lot for testing … Contractors want to use minimum cement in concrete.  Most structural engineers don’t specify minimum material in mixes (just strength).  If they required minimum mixes fewer issues would arise, but jobs would cost more.

3Q.      What is the difference between a “restrained” and “unrestrained” structure, and how is the structure determined to be either?

3A.      This applies to a steel building and its method of design.  A composite steel structure with moment connections would be restrained.  A steel warehouse would be unrestrained.  The restrained/unrestrained issue usually comes up regarding fireproofing, which is different for each design method.

4Q.      Why is there a W8x10 across a single elevator shaft?

4A.      Counterweights on side (on single), or at end for multiple elevators, and to support guide rails for a rear door elevator to provide space for counter-weights and support rails.  Once could call for a compound bracket that would do both.

5Q.      What does it mean to be “spirally reinforced”?

5A.      For columns to have slinky-type continuous ties to increase stiffness ±10%

6Q.      What is an upset beam?

6A.      Poured flush with slab and balance above slab.

7Q.      When are buildings built on geo piers vs. caissons or just slab on grade?

7A.      Geo piers, caissons, piles, spread footings or mat are all foundation types.  The slab on grade is just a cover over the earth to walk on.

8Q.      Why do you have a removal slab over mechanical room?

8A.      To allow equipment that won’t fit down the access (or up the access for removal) to be installed or removed.

9Q.      In a flat slab structure, what does it mean to say:  to be top and bottom mat lapped alternating at mid-bay of span?

9A.      Instead of arranging reinforcing per typical flat slab details, bars are continuous with alternate splice locations to resist progressive collapse.

10Q.    Pull pockets & beam project in post-tensioning – what is the beam projection?  What if you put a column at the end of the PT beams; do you still need pull pockets?  Are there holes in the slab for pulling pockets?  How big is a pull pocket?

10A.    Beam projection is same as pull pocket.  You still need pull pockets if you put column at the end of the PT beams.  Yes, there are holes in the slab for pulling pockets.  A pull pocket is ±12”

11Q&A.          Vocabulary Questions

a.         soldier beam – vertical members driven / drilled into the ground to hold out earth and support lagging

b.         raker braced – using rakers (diagonal steel members to concrete heel blocks cast in excavation) to temporarily hold up S.D.

            c.         walers – temporary steel members across the face of S.D.

d.         garage interceptor – plumbing device to run garage drainage water through to remove oil before it goes into sewer

            e.         dwi-dag bars – high strength 1-1/2” deformed bars

            f.          RD, FD sweeps – roof drain, floor drain pipes

g.         cambered slabs – poured like a tent, with the center of each bay up; for steel, a member set up in the center (fabricated that way)

            h.         ceiling plenum – space between bottom of structure and suspended ceiling

12Q&A..         Please explain what the following measure and how they differ.

a.         Pachometer (profometer) – a magnetic device that you rub across concrete surfaces to locate metallic elements & their approximate size & depth, omni-directional

            b.         Ferroscan – similar to pachometer, but better & more expensive

            c.         X-rays – just as with your bones, looking for elements embedded in concrete

            d.         GPR – Ground penetrating radar, used to locate voids in concrete, earth, etc.

            e.         Soundings – resonance device looking for voids, rock depth, etc.

13Q.    How do you know which method to use & when? 

13A.    Cost and/or type of material being looked at, eg. post-tensioning

14Q&A.          What are the various methods of testing for concrete strength & how do you know when to use which method?

a.         Cylinder – sample taken during concrete pouring process, cured & broken in laboratory to demonstrate strength; used during job

b.         Schmidt Hammer – calibrated device bouncing metal ball off concrete to get an approximate strength reading; 1^st shot @ guessing strength

c.         Windsor Probe – shoots 3 nails into concrete to determine penetration & therefore strength; 2^nd shot

d.         Cores – samples drilled out of concrete; method per ACI for determining strength of poured concrete