ACROW Truss Rating

Back in March I finished a rating for an ACROW temporary truss located in Russell MA. The bridge was constructed in 1986, to allow access to a factory after truck traffic was stopped over a now closed three span arch. The bridge spans over the Westfield River near a large mill and dam.

The three spans consist of two double single reinforced and one double double reinforced trusses.

The rating was our first ACROW rating and was pretty complex, we were able to break the rating down into 6 different parts.

First we checked the deck which consists of several 2.33' x 4.97' panels that weigh 282 pounds.

Next we looked at the transoms (floorbeams) which we treated as a simple span between the two truss members.

After the transoms we looked at the shear at the pinned connections which are located at each truss panel.

We then looked at the shear at the supports looking at the top and bottom cords which consist of eight to twelve channels.

Then we looked at the flexure near midspan using the section modulus of the truss and the dead load and live load moments.

Finally we checked the buckling of the top cord which ended up being the most complex part of the rating.

The bridge is located in a beautiful area which I will have to visit again. 

Stone Masonry Arch Rating

 

Catching up, This August I worked on a MassDOT rating for a stone masonry arch in Uxbridge MA. The arch was built in 1900 and rehabilitated in 1936 and 1960 and spans 39.5 feet over the Blackstone River.

The 1936 rehabilitation consisted of adding a 1’-6” concrete slab in the spillway and pointing the arch ring. The 1960 rehabilitation consisted of adding concrete railings and concrete tie beams.

  

The stone masonry arch is founded on stone masonry abutments with concrete backing.

This was my first time rating a masonry arch but soon after I had to rate an unreinforced concrete masonry arch in Providence RI.

The rating took a few iterations but we were able to derive a complete rating that was well above the statutory loads.

For the inspection we were able to use a 62 foot under bridge inspection unit (UBIU) which was able to reach all parts for the arch.

After figuring out the soil pressure and the dead loads for the spandrel wall and pavement, I input them into STAAD to find the axial and moment coefficients.

Using the coefficients I was able to find the location of for the maximum reactions of the axles and then figure out whether the thrusts were located within the kern.