Regulatory trends 1

[gwynn]

Over the past few years we have seen increasing limitations on what contractors may do or have done to bridge girders. Some limitations have always existed in my experience. Eg. I have never seen a case where the designer or governing state/provincial body would allow someone to core through the web of a precast concrete girder and being allowed to field weld to a steel girder has always been a rare exception.

In the past few years the limitations have grown so that things such as having standard Dayton Richmond/NCA etc. inserts cast into precast girders is not permitted. Likewise with things like drilling into the top flange of a precast girder, shop welding extra studs to the top flange of a steel girder or adding bolt holes to a steel girder.

I have two questions related to this:

First, are anyone else's experiences the same?
Second, what is driving the changes?

 

[Drumchaser]

In my region, I am not aware of ever being allowed to drill into the top flange of a precast girder or adding bolt holes to a steel girder. The standard drawings generally cover most needs.

My question would be why would you need to do these things.
Our standards cover inserts to be cast in conc. girders for overhang, edge forms, and re-stl for different flavors of bridge rail.
I do realize DOT's vary quite a bit from area to area, but can understand the EOR not wanting to have the beams carved on.
We routinely make air splices on steel girders, but I do not think this applies to your "field weld" comment.

The girders we use are, or at least used to be, the holy grail and are still generally treated as such.

 

[gwynn]

A couple of reasons we would do this are to support the deck formwork and provide stability during the deck pour.

Eg. typically deck formwork on a box girder bridge is supported by having inserts casts into the exterior face of the exterior girders. Of course, there are always contractors who don't get the construction engineers involved early enough (the girders are already cast), in which case the deck formwork is typically anchored to rods that are Hilti-Hit into the top flange of the box. Concrete I girders are similar, except that we would be going to the top of the top flange in both cases (unless there is interior formwork as well and the spacings are identical instead of having the interior at a multiple of the exterior).

On most design drawings I see, there is a clause in the notes saying that the stability of the girders during erection etc. is the responsibility of the contractor. When that note is present, it's not uncommon to see that the diaphragms spacing is such that extra diaphragms are needed during the deck pour, the diaphragms themselves are inadequate for the forces they attract during the pour or they have been designed such that they are only useful as diaphragms once the deck has been cast (eg. concrete diaphragms where the only rebar is in the bottom 6"). Though when this is the case, generally all those clauses about not bolting to girders or coring into them get thrown out the window.

Other examples would include anchoring lifelines, adding lifting lugs to steel girders, moving the point of load from the formwork away from the edge of the flange on NU girders or adding bracing to steel girders so they can be launched instead of crane erected.

It is not the EORs who have made the changes to what is permitted, it has all be done by state/provincial bodies. Where things like providing additional inserts in girders or coring into them is still permitted by the regulatory bodies, I rarely have the EOR say no.

 

[Drumchaser]

The box girder inserts you refer to are taken care of by the beam supplier and folks at the casting yard. To my knowledge it is not permissible (in this area) to hilti drill into a box or I Girder without some serious mojo.

"stability of the girders during erection etc." - We utilize minimum erection and bracing standards which covers (if done properly) stability during/after beam placement and during concrete deck pour.

As far as fall protection cables, handrail etc., we utilize the beams exposed re-steel (U bars etc.) if possible, or incorporate overhang brackets into the system.

Are you regulated by a state DOT?

Have heard of Girders being launched but not seen it done.

Not disputing your reasons for massaging the girders...just surprised it is/has been allowable.

 

[gwynn]

I haven't paid attention to this thread recently, but to respond:

Where required for formwork/falsework provisions, the inserts are specified by the construction engineer here. The folks at the precasting yard install them only. I assume that was what you meant, but I just wanted to be clear. However, due to the regulatory changes we have been seeing, having inserts for formwork installed by the folks at the precasting yard (or anyone else) is not permitted in some locations.

I am curious on what those bracing standards are. I know some DoTs have prescreptive bracing requirements for girders prior to and during the deck pour (eg. things like ties between studs or stirrups at every x distance). When I see these recently, I always wonder how often they are updated, since in the last ten years we have seen overhang widths and deck finisher weights increase dramatically. On type V AASHTO girders and steel girders typical overhangs used to be in the three to four foot range, with the maximum being around five feet. Now we routinely see deck overhangs of eight feet or more. Over the same period of time the typical deck finisher weight has more than doubled (the older finishers were usually pushing 5000lbs an end while we have seen weights up to 15,000lbs an end recently).

At the same time, I have yet to see somewhere with standards that do not say that the designer shall take into account the loads during construction during the design and in every case have seen designs that do not adequately account for the torsion on exterior girders during the deck pour. That is not to say that all or most designers neglect this, but it is a fairly common occurence. In recent years, part of this has been due to the aforementioned increase in deck finisher weight - it's not uncommon for the expected finsher weight to be given on the drawings and nine times out of ten it is low now.

In the places where this is an issue, attaching even single point tie offs to the stirrups is unaccceptable as the stirrups are epoxy coated and doing so could damage the coating.

Everything we do in this regard is regulated by either a state DoT or provincial MoT.

Launching is uncommon, but not rare if you do work outside of urban areas. I average roughly one launch design a year.

The frustrating part is not knowing the reasoning behind the changes, not having any input/conversations with those making the changes and the vast differences between jurisdictions. I have five ongoing construction projects in three different jurisdictions. There are overlapping design firms and design teams between them. In one area the contractors cannot have inserts cast into the girders, cannot Hilti into them or weld to them unless there are problems with the existing diaphragms and cannot leave any steel within the deck that is not specified on the design drawings other than formwork hangers. In the second, the contractors can have inserts into the girders, have the same restrictions on coring and welding and can leave steel in the deck as long as it is glavanized. In the third the contractors can have inserts cast into the girder, can Hilti into the top flange of precast girders, weld extra studs to steel girders and leave extra steel in the deck as long as it meets cover requirements. The bridge designers will and have approved all of these items in each case, it has only been the regulatory body that has said no.