Construction of Bents

Joshua Black and Sharon Wood

Department of Civil, Architectural and Environmental Engineering

University of Texas at Austin

Overview

• Site layout• Construction • Material properties

Site Layout

• Map of Austin• Plan of site• Photograph of site• Location of shafts and bents

Fitzpatrick Ranch

Fence

Borehole S1Depth: 14.5 ft

SPT Borehole D1Depth: 36 ft

Borehole S2Depth: 9.5 ft SPT Borehole D2

Depth: 36.5 ft

Test Site: 60 x 50 ft

Test SiteMagneticNorth

Fitzpatrick Ranch

View from South

View from North

Fence

MagneticNorth

Bent 1

Bent 2

40 ft

15 ft

15 ft

1W 1E

2N

2S

Test Site

ProjectNorth

Bent 1

Bent 2

Shaft 1W Shaft 1E

Shaft 2NShaft 2S

Construction

• Shaft/column reinforcement• Drilled shafts• Formwork• Concrete placement in shaft/column• Construction of bent caps

Shaft/column reinforcement

• Reinforcing cages were fabricated in Ferguson Structural Engineering Laboratory

• Strain gages and geophones were attached to cages

• Complete cages were transported to site

Shaft/Column Reinforcement

16 - #3 Bars

12 in.

¾ in. CoverW2.9 Spiral1¼ in. pitch

Clear spacingbetween bars = 3.3 in.

Column diameter

Drilled Shafts

• Commercial drill rig was used

• Shafts were larger in diameter than anticipated

―Desired diameter = 12 in.

―Actual diameter ≈ 18 in.

• Caving of soil was observed in all shafts

Shaft 2N

Shaft 2S

Formwork

• 12-in. Sonotubes were used above grade

• Sonotubes extended approximately 7 in. below grade

• Cages were centered within shafts

• Formwork was supported at grade and near top.

• Cables for strain gages and geophones were positioned outside the formwork before placing the concrete

Formwork at Grade

A A

Plywood Base Plate

2x4 Collar

Cardboard Tube Form

2x4 Collar

Plywood Base Plate

Cardboard Tube Form

Approx.7 in.

Edge of Hole

Concrete(Reinforcing cage is not shown)

Section A-APlan View

Shaft 2N

Bent 2

2N 2S

Bent 1

1E

1W

Concrete Placement in Shafts

• Ready-mix concrete was placed using a concrete pump

• Concrete vibrator was used at grade and at the top of the shafts

Bent Caps

• Reinforcing cages for bent caps were tied on site

• Concrete was placed using a front-end loader

• Threaded rods were cast in the bent caps to apply lateral forces during static tests

• Adapter plate designed to accommodate the shaker from Thumper was embedded in fresh concrete

Material Properties

• Concrete (Shafts, Columns, and Beam)― = 7200 psi― = 4600 ksi

• Steel (Shafts and Columns)― = 60.8 ksi― = 102 ksi

• Soil―Nonplastic silt―Documented in site characterization report

(Kurtuluş, Lee, and Stokoe, 2005)

cf

cE

yf

uf

Josh Black, MS 2005