Construction of Bents Joshua Black and Sharon Wood Department of Civil, Architectural and...

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