Written By: Jim Klinger, Concrete Expert
Question: We have an opportunity to bid a portion of the reinforced concrete scope on an upcoming industrial/manufacturing plant and adjacent support building project (e.g. parking garage and two steel office buildings) which is slated to break ground next month. The Owner is releasing the work in phases (aka "bid packages") driven by structure type, material availability, Owner financing, and seasonal weather considerations consistent with the jobsite geography. For this project, the Owner envisions having the reinforced concrete foundation portions of each structure "in place and cured" before winter sets in. In our case, the task at hand is to prepare a price proposal for "Bid Package #1: Early Foundations".
According to project details advertised by the general contractor (GC) during last week's pre-bid conference, the foundations we are to bid include a reinforced concrete mat foundation for the post-tensioned (PT) parking garage; and reinforced concrete pile cap/grade beam systems for the manufacturing plant itself and its two adjacent mid-rise structural steel support buildings. According to the Owner's schedule, once the foundation mat for the PT garage is in place, construction of the upper floors can proceed through the winter months as long as we follow the approved cold-weather concrete construction plan we are required to submit as part of our Bid Package #1 scope.
In other words, construction of the PT garage can proceed as normal, with no interruptions. But the ongoing design of the structural steel frame for the manufacturing plant introduces potential schedule hiccups into the equation. According to the design team, the design of the upper portion of the steel frame is partly dependent on the vibration loads introduced into the base structure by the manufacturing equipment. That equipment is still in the design phase overseas (Germany).
In his presentation at the pre-bid conference, the structural engineer told us the Owner expects further delays once the manufacturing plant equipment is fully designed due to reported material supply chain--and even potential tariff--issues. Nevertheless, the Owner wants to hedge his bets and have the foundation for the manufacturing plant in the ground as soon as possible.
Normally, our traditional scope of construction services only includes work items directly related to reinforced concrete construction. For example, we include structural excavation of spread footings, but we exclude mass excavation and offhaul of spoils. We include localized dewatering--in an elevator pit, for example--but we exclude mass geotechnical dewatering. We include setting of almost all items shown to be embedded in the concrete that we place, but we do not supply any embedded items.
On this project, however, the Owner is "calling an audible" and requiring the concrete Bid Package #1 bidders to include the furnishing of structural steel anchor rods, weld plates, embedded plates, embedded shapes (e.g. small lengths of W-shapes or channel shapes as shown) and so on into our scope. Ordinarily, such a scope would be picked up by the structural steel supplier, or even the structural steel erector.
Our initial reaction was "Why doesn't the GC solicit bids for the supply of the embedded steel items? The GC's position: the concrete contractor must become familiar with the embedded items anyway--quantities, types, sizes, locations--in order to price their setting. Once quantities and types are known, soliciting prices should be the logical next step. Since we anticipate being asked to bid on subsequent bid packages on this project over the next few years--including a substantial site concrete scope--we decided to take on this task of embed supply for the embeds that are shown to be set in the manufacturing plant pile caps, grade beams, and slab on grade. And that business decision is what has prompted our call to the ASCC Hotline.
During the design team's presentation at the pre-bid conference, the structural engineer made several emphatic comments regarding the grade of structural steel. Example comment: "Make sure that the steel that is used in the fabrication of the embedded shapes has been fully killed."
Questions to the Hotline then become:
--What is fully killed steel...and how could killed steel affect our price?
Answer: This is an item that might be worthy of a pre-bid RFI to the structural engineer. By all rights, the structural construction documents (usually the "General Notes" sheets) should identify the American Society for Testing and Materials (ASTM) Standard grade for each of the various structural steel members to be used in the project--including embedded steel material. Concrete contractors should already be familiar with commonly used ASTM steel grade designations such as ASTM grade A36, for example, or ASTM grade A572. Therefore, when your estimator is tabulating the embedded item quantities in a spreadsheet, we suggest creating a column that lists the ASTM Standard grade for each embed mark for material tracking and pricing purposes.
The term "killed steel" is not new to the industry, and is related to the chemical composition--and behavior--of the steel as it is produced from molten to hardened (cast) material in the steel mill. The idea is to deoxidize the steel by adding either Aluminum (Al) or Silicon (Si) while the steel is still molten. Once the steel is ladled (cast) into the molds, the added Al or Si keeps the material from developing gas bubbles during solidification. Since the steel essentially lays still in the mold (no gas bubbles develop), it is then said to have been "killed". The end result is steel with less porosity.
The requirement for killed steel appears in ASTM A992: Standard Specification for Structural Steel Shapes, section 4.1 as follows:
"The steel shall be killed, and such shall be confirmed by a statement of killed steel on the test report, or by a report on the presence of a sufficient quantity of a strong deoxidizing element, such as silicon at 0.10% or higher, or aluminum at 0.015% or higher."
Any cost impacts will have to come from your steel supplier of choice. The key is letting your supplier know what material has been called out as ASTM A992 (as opposed to, say, ASTM A36 or ASTM A572 material, for example) so they can advise you if there is any price impact. We suggest you supply the project bid documents to each steel supplier and you can compare their estimate with yours. After that exercise, a pre-bid RFI to the design team probably won't be necessary, since any "premiums" will already be rolled into the supplier's pricing to you.
Question: Is there any document that says footings must be formed and not trench poured? Is this part of any Code that you are aware of? We have a township official telling us this is an ACI requirement.
Answer: The above Hotline questions originally appeared in the October 2012 ASCC Voice newsletter. A link to an updated version of the 2012 original Voice article can be accessed online here:
Updated Article Here.
In addition to the update of the original 2012 article, what follows below are supplemental comments that reflect document changes, Code updates, and knowledge gained from 13 years-worth of field experience.
At issue is the question that all concrete estimators ask themselves when the structural drawing foundation plans are unrolled on day one of the quantity takeoff for a new concrete construction project: "will we have to form the vertical foundation sides, or will the jobsite soil conditions (or design requirements) allow us to cast the foundation concrete directly against earth?"
(N.B.: Although we have not seen this explained in the current literature, the so-called "neat-cut" method is almost always going to benefit the Owner in terms of time and dollars. After all, the "formed sides" option has several activities that the neat-cut method does not have, namely over excavation, furnish formwork material, erect foundation side forms, strip form sides, patch formed faces (if needed), and backfill/compact soil against the formed sides.
The downside of neat-cutting, of course, is risk. Once you commit to neat-cutting in your bid proposal, you own the work whether it ends up being neat cut or formed.)
The first step in answering the question of whether or not to form foundation sides is to examine the bid documents to determine if the design team has somehow prohibited the so-called "neat-cut" method of casting foundation concrete directly against earth. Such prohibitions might appear in typical drawing details or in specific section cuts taken through the foundation. We have also seen such prohibitive requirements expressed in project specifications.
The second step is to carefully examine the soil borings and recommendations that appear in the project geotechnical report (aka the "soils report"). Certain soil conditions--borings that reveal dry, loose, sandy soil, for example--are quick indicators that the footing sides cannot stand after excavation without sloughing and collapsing.
The third step is to carefully examine the construction documents for waterproofing requirements, if any, that can be a factor when sides of the foundation elements (including elevator pits) are to be formed. In many cases, once forms are stripped, supplemental patching may be required to accommodate follow-on waterproofing applications. We recommend the bid team review ASCC Position Statement #27 Formed Surface Requirements for Waterproofed Walls if foundations require forming.
A link to the latest ASCC Position Statement #27 is here:
https://ascconline.org/Portals/ASCC/Files/Position%20Statements/PS-27_FormedSurfaceRequiremts_webSC-1.pdf?ver=U7QefaD9st_owBZfsZPwHA%3d%3d
Although the ACI Code is silent regarding forming of foundation sides, the International Building Code (IBC) is not. IBC 2021 section 1808.8.5 Forming of concrete states:
"Concrete foundations are permitted to be cast against the earth where, in the opinion of the building official, soil conditions do not require formwork. Where formwork is required, it shall be in accordance with section 26.11 of ACI 318".