I currently have a gravel driveway that I would like to upgrade to concrete. It has had several layers of gravel over the decades and been driven on for at least 50 years. Any concrete slab on grade I have ever designed has always included a gravel base over the subgrade. However, I am thinking...
We have a large concrete placement planned and the contractor wants to use 2 different batch plants. The issue is each plant has a different proposed mix. Each mix by itself would be acceptable but I don't know if it would be a good idea to mingle the 2 mixes. One mix proposes the use of Type 2...
I cannot find our office copy of the 1993 AASHTO PDG and have been asked to do a small pavement design. What I really need is Figure G.7 and Figure G.8 from Appendix G. If someone could scan them for me I would really appreciate it. Thanks!!
I am doing a pavement design and cannot find our 1993 AASHTO Pavement Design Guide. What I really need is Figure G.7 and G.8 from Appendix G so if someone could scan them for me I would really appreciate it. Thanks!
I have a small building with CIP concrete walls and a CIP suspended slab. The building is roughly 27'X22' in plan size. The contract called for 3750 psi concrete and the slab was designed with f'c of 3500 psi. The cylinders broke low so we had cores taken. The cores broke at an average of about...
Has anyone ever placed P/S strands in the top slab of a box beam? I have a project that requires 33-48"X17" adjacent P/S box beams. I have transverse post tension tendons at each end of the beams. Due to the large number of beams, I need staged construction to install the transverse tendons. My...
I am designing improvements to an existing retaining wall that is located along a City street and acts as a shoreline wall with a beach on the front and the street behind it. The wall is from 3 to 10 feet high. There is a 6 foot wide sidewalk immediately behind the wall. There is an existing...
I have a project going on right now that had a concrete pour last week where the entrained air content was consistently low. The plant kept adjusting the AEA(air entrainment admixture) but still stayed on the low side. The contractor has asked me if we still low air on the additional pours if he...
First off, I am not a mechanical engineer. I'm a structural engineer and my last exposure to anything like this was a course in structural dynamics in grad school 35 years ago. What I have is a centrifuge which rotates at 3200 rpm which is going into a wastewater plant. The centrifuge, which...
What is everyone's thoughts on placing sawcut contraction joints in suspended slabs? I routinely place them in slabs on grade but am unsure about the wisdom of placing planes of weakness in a structural slab. Most of my suspended slabs are designed with integral beams and removable forms and are...
I have a project where the 28 day concrete cylinders on 1 particular pour came back with substandard breaks(3278 psi for a 3750 psi mix). The contract documents require cores be obtained and tested and based on the cores the concrete either rejected or paid for at a reduced rate. I've already...
Does anyone know of a widely recognized reference(ACI,PCA,etc.) that discusses the effect that prolonged mixing time has on concrete strength? I know most specs. limit mix time to about 1.5 hours but I believe this is primarily to avoid having to add additional water to maintain workability. I...
I design a lot of liquid containing sanitary structures and our standard construction joint detail has always used PVC waterstops. The PVC waterstops are quite labor intensive to install, kind of messy at intersections and always leave some doubt as to how well they remain positioned during...
I have a client who is planning an addition to a building which will result in an exterior, load bearing wall which will be 50' long and about 20' high. He would like to use CMU's up to about 10' high and then wood framing the rest of the way up. The roof trusses will set on the wood framing...
Are there any codes such as the IBC which require plain masonry, simple 1 story block buildings to be anchored to the foundation? We typically have a wall footing with a cast-in-place concrete foundation wall on which the masonry blocks are set without any sort of anchorage and I was wondering...
Hi all, I'm a new member with a pretty basic design question. When designing the bottom slab of a buried tank which will be subject to uplift due to high groundwater, do I add the uplift force to the soil pressure due to gravity loads or subtract it? For example, If I have a 10 ft. by 10 ft...
