Structural Engineering: The Design of Sky Scrapers and Foundations. Isaac Gaetz SE PE LEED AP Structural Engineer

A little about me: Licensed Structural Engineer Education: Bachelor Degree in Civil Engineering Masters Degree in Structural Engineering Design structures (buildings, bridges, power plants, retaining walls, foundations) Located in Chicago 33 years Old

My Company CCJM – consulting engineers Engineer buildings, bridges, water treatment facilities. Green Engineering Minority Owned Business Established in 1979 Offices in Chicago, Camp Hill PA, Washington DC, Baltimore MD and Honolulu HI About 100 employees

A few of our recent projects…

Chicago Helicopter Experience

Schuylkill River Bridge, PA

Detroit Water Treatment Plant

Projects done with other companies…

One Museum Park East and West

353 N Clark

K2

Structural Engineering Load analysis – What sort of loads must a structure be designed to resist? Dead Loads (The weight of the structure itself) Live loads (The weight of people, furniture, cars/trucks, etc) Weather Loads (Snow, Rain, Wind, Earthquakes, Earth Pressure)

Structural Engineering Structural Design – How do we define a successful structural design? (how do we know we did a good job?) Structure is Safe (No Collapsing Allowed!) Structure performs well (No sagging floors, shaking or vibrations) Easily constructed (Fast and repeatable) Economical Design (Not wasteful of material or requiring excessive labor because labor= Cost) Aesthetically Pleasing (Achieve architectural vision)

Structural Engineering Structural Communication – How do we communicate our designs? (What is our work product?) Structural Calculations (must be organized, clear and complete. Calculations are done by hand and using advanced computer software.) Structural drawings (traditionally done by hand, but are now done in Autocad or Revit) Technical writing (Specifications, letters, emails, etc. An engineer must be able to communicate effectively to professionals and lay people.)

Foundation Engineering What common types of Foundations are there? Caissons (Vertical shaft is drilled and filled with a reinforced concrete “column” to carries loads in friction and bearing. Shallow Footings (Rely on Footing Bearing on Soil to carry structure. Now made of Concrete, but historically made of Masonry or even Timber. Must bear below frost depth. Driven Piles (Metal, Timber or Concrete shafts are pounded into the ground using heavy equipment. Load is carried with tip bearing and side friction)

Shallow Foundations

Deep Foundations

Foundation Engineering How do we design a structural foundation? Load Takedown (Calculate loads on Foundations) Geotechnical Report (Boring Logs, Bearing Capacity, Soil composition) Size footing using structural analysis techniques.

Shallow Foundation Design Example (Part 1): A 60’ x 60’ Single Story Concrete Building with Columns at 30’ On Center

Shallow Foundation Design Example (Part 2): Step 1: Use building Code to determine loading foundation needs to carry. (100psf Dead Load and 30psf Snow Load.) Step 2: Compute tributary area of column and foundation. (Columns at 30’ O.C., Tributary Area 900sf) Step 3: Multiply Tributary Area by Loading to determine foundation load. Tributary Area x Required Loading = Foundation Load 900SF x (100psf +30psf) = 117,000lbs 117,000lbs = 117kips Step 4: Divide foundation load by allowable soil bearing capacity to determine required footing area. Foundation load / Allowable Bearing = Required Footing Area 117kip / 3ksf = 39sf Step 5: Size Actual footing based on required Footing Area. Actual must be equal to or greater than required footing area. Typically foundations are sized to the nearest 6”. Try 6’-6” x 6’-6” Square Actual Footing Area > Required Footing Area 6.5ft x 6.5ft > 39sf 42.3sf > 39sf Actual is larger than required, design is OK!

Deep Foundation Design Example (Part 1): Design of a 60’ Caisson, with a 6’ Diameter Main shaft and 12” Diameter Bell.

Deep Foundation Design Example (Part 2): Step 1: Use building Code to determine loading foundation needs to carry. (The Foundation Needs to Carry the Tributary Area of All the Floors Above.) Step 2: Compute tributary area of column and foundation. (Columns at 30’ O.C., Tributary Area 900sf x 50Floors) Step 3: Multiply Tributary Area by Loading to determine foundation load. Tributary Area x Required Loading = Foundation Load 900SF x (80psf + 20psf) x 50 = 4,500,000lbs 4,500,000lbs = 4,500kips Step 4: Foundation Load is carried through both soil friction and tip bearing of deep foundation. (Caisson Diameter is typically dictated by available equipment.. Assume a 6’ Diameter Caisson.) Determine Friction Capacity, Caisson Surface Area x Friction Coefficient Pf = 6’ x π x 60’ x 2ksf Pf = 2,260kips Bearing Area must carry Load not carried by Friction 4,500kips – 2,260kips = 2,240kips Step 5: Multiply Caisson Bearing Area by Allowable Bearing Capacity to determine how much load is carried in Bearing Try a 12’ Diameter Caisson Diameter Footing Area x Allowable Bearing = Bearing Capacity 113sf x 20ksf = 2,260kips > 2,240kips. Design is OK!

Soils and Foundation Failures

Who should be a structural Engineer? People interested Construction and Technology. Strong Math, Science, Reasoning and Logic skills. Problem Solvers. Enjoy a mix of office and field (outside) work. Good communicator - Writing, Drawing, and Speaking. Likes working collaboratively Question 1: If I’m not good at Math, should I be an Engineer? Answer: Math is a skill and a tool. Like all skills, you can become better at math with hard work and practice. Some engineers use complex math everyday of their careers, others rarely do. There is more than one path in engineering. All engineers must be able to communicate. Question 2: What can I do now to prepare to be an Engineer? Studying hard is always a good place to start. Try to learn about construction and how things are built. Fix things around your home, read books on construction. Design (carefully draw and dimension plans) and Build something. Start small and build from there. Even skyscrapers start small.