Limit States [SIG]

Each row in OpenBrIM generates two linear result combinations: one with maximum factors and one with minimum factors. The calculation of the factored DC1 involves multiplying load modifiers (ηD * ηR * ηI) with the maximum load factor (γ max). These values are then added to other factored loads, such as factored DC2, DW, LL, etc., to obtain the final maximum result. The calculation of the factored DC1 for the minimum load factor (γ min) is done using the same load modifiers. These values are then added to other factored loads to obtain the final minimum result. Therefore, the terms "max" and "min" refer to the load factors being used in the calculation.

When viewing results in spreadsheets, users have the ability to see positive and negative live load results with maximum or minimum factors. The terms "positive" and "negative" are used for live load and wind load envelopes, where we try to maximize the negative value or maximize the positive value. The terms "min" and "max" refer to the factors.

Definitions for Limit States

There are two ways to define the limit states and their related coefficients in this section:

• Users can manually define each cell.

• Users can import data from the OpenBrIM database.

To import from OpenBrIM Database:

Open

On the related cell, click the three dots, then choose Import OBPAASHTOLimitState

Open

Then, in the window, specify the limit state to be imported by selecting the Database, Category and Asset inputs.

 

 

Load Modifiers

ηD: a factor relating to ductility, as specified in AASHTO Article 1.3.3

ηR: a factor relating to redundancy, as specified in AASHTO Article 1.3.4

ηI: a factor relating to operational classification, as specified in AASHTO Article 1.3.5

The combined results are multiplied by ηi=ηD*ηR*ηI (load modifier: a factor relating to ductility, redundancy, and operational classification). According to AASHTO 1.3.2.1-2, ηD*ηR*ηI should be greater than or equal to 0.95.

Load Case 1

Each row in this section corresponds to a particular limit state, such as Strength 1, Service 1, Extreme Event 1, and Fatigue 1. If the user needs to define different factors for substructure code check and superstructure code check for the Strength 1 limit state, two rows should be defined, namely Strength 1 (Sub) and Strength 1 (Super).

DC1 (Noncomposite Dead Load): Loads that are applied to the non-composite state of girders, such as self weight of steel girder and cross frame load, formwork load, and deck load, should be mapped to this category.

γ max: Typically 1.25 for strength limit states. Maximum Load factor per AASHTO Table 3.4.1-2/DOT amendments.

γ min: Typically 0.9 for strength limit states. Minimum Load factor per AASHTO Table 3.4.1-2/DOT amendments.

DC2 (Composite Dead Load): Loads that are applied to the composite state of girders, such as barrier loads should be mapped to this category.

γ max: Typically 1.25 for strength limit states. Maximum Load factor per AASHTO Table 3.4.1-2/DOT amendments.

γ min: Typically 0.9 for strength limit states. Minimum Load factor per AASHTO Table 3.4.1-2/DOT amendments.

DW (Wearing Surface-Utilities): Loads that are applied to the composite state of girders, such as wearing surfaces and utilities loads should be mapped to this category.

γ max: Typically 1.5 for strength limit states. Maximum Load factor per AASHTO Table 3.4.1-2/DOT amendments.

γ min: Typically 0.65 for strength limit states. Minimum Load factor per AASHTO Table 3.4.1-2/DOT amendments.

Users can follow a similar approach to assign appropriate values and result cases for the parameters listed below.

LL (Vehicular Live Load):

γ max:

γ min:

LL (Vehicular Braking Load):

γ max:

γ min:

WS (Wind on Structure):

γ max:

γ min:

WL (Wind on Live Load):

γ max:

γ min:

TU (Uniform Temperature):

γ max:

γ min:

CE (Vehicular Centrifugal Load):

γ max:

γ min:

CL (Construction Loads):

γ max:

γ min:

Load Case 2

EV (Vertical Earth Pressure):

γ max:

γ min:

PS (Prestress Load):

γ max:

γ min:

PL (Pedestrian Live Load):

γ max:

γ min:

TG (Temperature Gradient):

γ max:

γ min:

WA (Water Load and Stream Pressure):

γ max:

γ min:

IC (Ice Load):

γ max:

γ min:

EQ (Eartquake Load):

γ max:

γ min:

CT (Vehicular Collision Load):

γ max:

γ min:

CV (Vessel Collision Load):

γ max:

γ min:

LS (Live Load Surcharge):

γ max:

γ min:

Load Case 3

SE (Settlement):

γ max:

γ min:

ES (Earth Surcharge):

γ max:

γ min:

EH (Horizontal Earth Pressure):

γ max:

γ min:

EL (Locked-in Loads):

γ max:

γ min:

CR (Creep Load):

γ max:

γ min:

SH (Shrinkage Load):

γ max:

γ min:

DD (Drowndrag Load):

γ max:

γ min:

FR (Friction Load):

γ max:

γ min:

BL (Blast Load):

γ max:

γ min: