108 Delancey StreetLower Eastside Manhattan

April 4, 1984

By: David M. Ulrich and Keith MalmbergDrawings by David M. Ulrich in AutoCAD

2010

Purpose : To retrofit a concrete masonry unit (CMU) and wood floor construction building with structural steel and concrete slab on metal decking

DMAConsultants and Construction Managers

1st Floor

2nd Floor

3rd Floor

4th Floor

5th Floor

Cross section of existing building

• Five floors of wood flooring (beams/joists)

Building 1 Building 2

• Two buildings share central load-bearing wall

• Building 1 and Building 2 interiors are completely separate

• Current system utilizes continuous CMU stem wall footings

1st Floor

2nd Floor

3rd Floor

4th Floor

5th Floor

Proposed Retrofit Agenda

• Remove 2nd Floor and Central CMU bearing wall

Building 1 Building 2

• Replace 1st floor with structural steel and slab-on-metal decking

• Retrofit continuous stem wall footings into three main spread footings

• Utilize wide-flange columns, beams, and girders in lieu of structural masonry

• Removal of 2nd floor resulting in large space with vaulted ceiling

Cross section of proposed retrofit

2nd Floor

• Installation of three spread footings into existing bearing wall (Epoxy Installation)

• Support the multi-wythe CMU bearing wall from 3rd Floor to Roof

Base Plate with(4) 3/4" Threaded rods

W10x49 ColumnW12x26 Beam

3 1/2" conc. slabon 22ga. metal deck

W12x50 Girder

Steel retrofit design

Here are some basic components of the proposed retrofit design

W 12 x 50What Does This Mean?

12” Flange-to-Flange dimension

50 lbs per linear foot

W Shape

13" UNO 10" min embed

Footing to steel column connection

Concrete Slab-on-Grade

Wide Flange column

Spread Footing

Non-shrink groutBase Plate + Threaded Rods

Footing Installation

Subgrade assessment

Form Installation

Undisturbed Native Soils?No

Firm and Unyielding Soils?

Use a flat bucket for excavation

Replace soils removed

Footing Dimensions

Location

No

Over excavate to dense soils

Adequate form bracing to support lateral load of concrete

Ensure column will load footing as designed

1

2

Spread Footing Concrete Placement

1

2

3

Secure rebar prior to concrete placement (3” from earth per ACI)

Place anchor bolts correctly in relation to the rebar mat per plans

Mechanically consolidate concrete with a vibrator

4 Leave adequate clearance below base plate template for non-shrink grout

3 Inches

Footing ‘spreads’ load from the footing bottom to earth beneath

Notice the column assemblyIn the center of the footing

Correct Spread Footing Load Path

Spread Footing Loading

OK NOT OK NOT OK NOT OK

1 2 3 4

GOODBAD

Eccentric LoadingStandard Central Loading

To Remove Floor #1 and #2 we will need Shoring.

• Floors need to be shored prior to removal of load-bearing wall sections

• Shoring can be rented until concrete has reached full strength and is adequate for support

• Falsework of this magnitude is not to be ‘site-designed’ by a contractor.

• Consult with an engineer for shoring design

Adjustable screw with baseplate

108 Delancey Street

12" CMU Block Wall

8" CMU Block Wall

Spread Footings

104 Delancey St 106 Delancey St

5 S

torie

s A

bove

Concrete stem wall foundation and Concrete Masonry Unit walls (CMU blocks)

Three critical spread footings along shared central wall

Multi-wythe CMU walls of different block width

1

2

3

Floor Plan

A

B

C

A vague list of what went wrong

• Lack of field supervision and inspection oversight• Lack of step-by-step construction sequence resulting in lateral instability• No shop drawings

• Spread footings were installed incorrectly• Spread footings were installed below 50% of design strength

• Spread footings were eccentrically loaded

• Shoring schedule out of sequence• Removal of 3rd floor and pouring one side created a twisting force

• Lack of lateral support coupled with eccentrically loaded footings created an inevitable collapse

What went wrong with the footings?

• Footing dimensions were installed wrong (contractor at fault)

• Footing were eccentrically loaded (contractor at fault)

Actual footing installationA

B C

• Some of the footings were less than 40% design size

Did the contractor have structural plans?

Footing dimensionsAS DESIGNED BY ENGINEER

Footing Length Width Ft2 % Design

A 8'6 5'6 47 ft2

44%A 4'8 4'7 21 ft2

B 5'6 7'0 39 ft2

51%B 5'9 3'6 20 ft2

C 5'6 7'0 39 ft2

36%C 4'2 3'4 14 ft2

Designed Footing DimensionsInstalled Footing Dimensions

44%51% 36%

What went wrong with the shoring?

1. The contractor removed both sides the 3rd floor

2. The contractor only poured back one side of floor 3

3. Floor 3 had no lateral stability when it began to twist

THE END