Progressive Collapse Considerations in the Design of ...redsismica.uprm.edu/.../Montejo/Montejo_Progressive_Collapse_2012.… · Progressive Collapse Considerations in the Design

Progressive Collapse Considerations in the Design of Structures for Vertical Evacuation

from Tsunamis

Luis A. Montejo, PhD Assistant Professor, Engineering Science and Materials, UPRM

Workshop on Vertical Evacuations from Tsunamis Colegio de Ingenieros y Agrimensores de Puerto Rico

18 al 20 de junio de 2012 San Juan, Puerto Rico

1962 Ronan Point Apartment Tower Collapse (London)

Pearson and Delatte, 2005 Choi and Chang, 2009



Partial collapse of the structure killed 4 people and injured 17

The collapse sheared off the living room portion of the apartments, leaving the bedrooms intact with the exception of floors 17–22, where all the fatalities occurred.

The explosion was not significant in magnitude < 70 kPa (10 psi).

The tower consisted of precast panels joined together without a structural frame.

The connections relied mostly on friction.

The apartment tower lacked alternate load paths to redistribute forces in the event of a partial collapse.

Poor workmanship at the critical connections between the panels.

Progressive and disproportionate collapse definitions

“Progressive collapse is the collapse of all or a large part of a structure precipitated by damage or failure of a relatively small part of it. The phenomenon is of particular concern since progressive collapse is often (though not always) disproportionate, i.e., the collapse is out of proportion to the event that triggers it. Thus, in structures susceptible to progressive collapse, small events can have catastrophic consequences.” Shankar Nair (Progressive Collapse Basics)

Ronan Point Collapse

Progressive

Disproportionate

1995 Murrah Federal Office Building, Oklahoma City

Courtesy of Applied Science International

1995 Murrah Federal Office Building, Oklahoma City

The Murrah Building was a nine-story, conventionally reinforced (nonductile), concrete structure constructed during the mid 1970s

The truck bomb, estimated to be 1,800 kg (4,000 lb) TNT equivalent, was centered approximately 4 m (13 ft) from one of the building columns

Created a paradigm that guided research and development of new structural design guidelines

Murrah Federal Office Building

Progressive

Disproportionate

2001 (9/11) World Trade Center I, 2 and 7


Progressive collapse did NOT occur in the WTC towers, for two reasons. First, the collapse of each tower was not triggered by a local damage or a single initiating event. Second, the structures were able to redistribute loads from the impact and fire-damaged structural components and subsystems to undamaged components and to keep the building standing until a sudden, global collapse occurred.

The failure of WTC 7 was an example of a fire-induced progressive collapse… caused by a single initiating event-the failure of a northeast building column brought on by fire-induced damage to the adjacent flooring system and connections.

According to NIST (National Institute of Standards and Technology):


Progressive

Disproportionate WTC

1 a

nd

2

Progressive

Disproportionate

WTC

7

2007 Minnesota I-35 Bridge

Steel deck truss bridge with little or no redundancy

Progressively collapsed over the entire span due to gusset plate connection failure

2007 Minnesota I-35 Bridge

I-35 Bridge

Progressive

Disproportionate

Progressive Collapse & Tsunami/Hurricane/Flooding

2004 Indian Ocean Tsunami 2005 Hurricane Katrina

2011 Tōhoku earthquake and tsunami (Japan)

1st Ed. - 25 Jan. 2005 2nd Ed. - 14 Jul. 2009 (updated 2010) 3rd Ed. - 2013?

Designing to Resist Progressive Collapse

1st Ed. – June 2003

U.S. General Services Administration


Direct Design Methods

Alternate Path Method

Specific Load Resistance Method

Indirect Design Methods

Minimum Levels of Strength, Ductility

and Continuity

Tie Force Method (Vertical and

Horizontal Ties)

The Tie Force Method

Illustration from Deneke, 2005

In the Tie Force approach, the building is mechanically tied together, enhancing continuity, ductility, and development of alternate load paths.

Tie forces can be provided by the existing structural elements that have been designed using conventional design methods to carry the standard loads imposed upon the structure.


There are three horizontal ties that must be provided: longitudinal, transverse, and peripheral. Vertical ties are required in columns and load-bearing walls. Unless the structural members and their connections can be shown capable of carrying the required tie forces while undergoing rotations of 0.20-rad (11.3-deg), the longitudinal, transverse, and peripheral tie forces are to be carried by the floor and roof system.



The Tie Force Method (required tie strength)

The vertical tie must have a design strength in tension equal to the largest vertical load received by the column or wall from any one story, using the tributary area and the floor load wF

Internal ties:

Peripheral ties:

Floor load:

Alternate Path Method

Illustration from Deneke, 2005

In the Alternate Path method, the designer must show that the structure is capable of bridging over a removed column or section of wall and that the resulting deformations and internal actions do not exceed the acceptance criteria.

1. What elements to remove? 2. How to remove them (type of analysis)? 3. Acceptance criteria?

Alternate Path Method (Removal of elements)

Beam-to-beam continuity is assumed to be maintained across a removed column, i.e. remove the clear height between lateral restraints. For walls, remove a length that is twice the clear story height H. For external corners with intersecting walls remove a length of wall equal to the clear story height H in each direction.

Alternate Path Method (Removal of elements - location)

Exterior Columns Interior Columns

Remove one element at a time. For each plan location defined for element removal, perform analyses for: 1. First story above grade 2. Story directly below roof 3. Story at mid-height 4. Story above the location of a column splice or change in column size

Alternate Path Method (Types of Analyses)

1. Linear Static / 2. Non-Linear Static / 3. Non-Linear Dynamic

Linear Static

Limited to non-irregular structures or demand to capacity ratios (DCR) ≤ 2 Construct a linear 3D model with all primary components with the exception of the removed wall or column (no 2D model allowed). Load cases:

Adjacent and above elem. removed (displacement controlled)

Adjacent and above elem. removed (force controlled)

Gravitational elsewhere

Lateral

Alternate Path Method (Linear Static)

Force controlled and deformation controlled actions



Load increase factors for linear static analysis

mLIF is the smallest m of any member connected to the one removed, m is an indirect measure of the nonlinear deformation capacity of the component


Acceptance Criteria

Deformation controlled actions

Force controlled actions

Alternate Path Method (Non-Linear Static)

Create a non-linear 3D model without the removed element. The force-displacement behavior of all components shall be explicitly modeled, including strength degradation and residual strength, if any.

Strength reduction factors are applied to the nonlinear strength models of the deformation controlled components.

Apply the loads using a load history that starts at zero and is increased to the final values. Apply at least 10 load steps to reach the total load.


Load increase factors for non-linear static analysis

θpra is the plastic rotation angle given in the acceptance criteria tables in ASCE 41 for the particular element, component or connection; θy is the yield rotation.



Acceptance Criteria

Deformation controlled actions

Force controlled actions

Primary and secondary elements and components shall have expected deformation capacities greater than the maximum calculated deformation demands.

Alternate Path Method (Non-Linear Dynamic)

Same modeling requirements than for the non-linear static but this time include the element that will be removed.

Same load combinations but NO dynamic amplification factors.

Apply the gravity loads and lateral loads in steps to the entire model.

After equilibrium is reached, remove the column or wall section.

The duration for removal must be less than one tenth of the period associated with the structural response mode for the vertical motion of the bays above the removed column.

The analysis shall continue until the maximum displacement is reached or one cycle of vertical motion occurs at the column or wall section removal location.

Acceptance criteria is the same than for the non-linear static analyses.

Recent and Current Research Efforts

Effect of seismic detailing

Recent and Current Research Efforts

Force redistribution, slab contribution and catenary effects during progressive structural collapse

‘Collapse' by Fletcher Vaughan


Acceptance Criteria – Secondary elements

“All secondary components and elements must be checked to ensure that they meet the acceptance criteria. This can either be done directly for each component or element where displacements are known, or alternately, a second mathematical model can be constructed that includes the secondary components. If the model is re-analyzed with the secondary components included, their stiffness and resistance must be set to zero, i.e., the advantage of including the secondary components is that the analyst may more easily check the secondary elements deformations rather than perform hand calculations of the original model.”


Progressive Collapse Considerations in the Design of ...redsismica.uprm.edu/.../Montejo/Montejo_Progressive_Collapse_2012.… · Progressive Collapse Considerations in the Design

Documents