Constraints Files¶
Once the required reinforcement is calculated, the physical reinforcement elements have to be designed in such a way that it satisfies optimally the design constraints, code specifications, and other particular demands. Usually, the engineer has to evaluate all the possibilities based on his own experience and knowledge in order to determinate the most convenient solution.
One approach to access such kind of implicitly given knowledge is Expert System technology. Expert systems are regarded as branch in the area of Artificial Intelligence and are currently used in many fields of application like medical diagnostics or assembly layout of computers. One of the key assumptions in (rule based) expert systems is, that the knowledge of an expert can be expressed in IF … THEN … type rules. The system provides facilities to enter these rules by the expert in a very simple and accessible syntax, often similar to human language, which enables the expert to enter his knowledge without deeper programming skills. These rules are then processed by the expert system within the so-called inference engine in order to generate new conclusions or initiate certain actions.
The automatic generation of the 3D-rebar model in SOFiSTiK Reinforcement Generation follows this approach. Each step in the generation of the rebar model, like the determination of the rebar layout in the cross-section or the calculation of anchorage and laps can be controlled by rules.
For example, in order to control the diameter of the longitudinal bars in a beam, the user may define the following rules:
//$ range of allowed parameters for the diameter of longitudinal bars.
d_asl = [ 0.006, 0.008, 0.010, 0.012, 0.014, 0.016, 0.020, 0.025, 0.028, 0.032, 0.040 ]
//$ restrictions of the range according to the height of the cross-section
Is_Beam {
d_asl <= 0.028
Section_Height <= 0.50 : d_asl <= 0.025
Section_Height <= 0.40 : d_asl <= 0.025
Section_Height >= 0.50 : d_asl >= 0.016
Section_Height >= 0.80 : d_asl >= 0.020
}
According to the different requirements in the design process, there will also be different kind of rule sets for controlling the rebar generation. There will be rules for maintaining the design code regulations or rules which the user can define on a project or company specific basis.
Optimization¶
The definition of the physical reinforcement can be controlled by the engineer in order to optimize the automatic generation of the 3D rebar model and produce an outcome that satisfies several objectives.
The requirements of the engineer are captured by means of weighting factors which act on particular goals, increasing or decreasing their relevance during the generation process.
These factors are stored in the constraints file:
//$ weighting factors ( >1.0 increases effect, <1.0 decreases effect, 0.0 no effect)
//$ F1: try to use as less bars as possible (increase rather diameter than number)
//$ F2: try to reduce difference between inserted and required reinforcement
//$ F3: try to avoid using multiple layers of reinforcement (bending beams only)
//$ F4: prefer to use same diameter for base and supplemental reinforcement
//$ F5-F8: reserved
W_FACTORS = [ 1.0, 1.0, 1.0, 0.0, 1.0, 1.0, 1.0, 1.0 ]
Parameters¶
Definitions of predefined parameters which can be used in a constraints file in order to create or modify design rules are listed in the following.
Note
The parameter’s input is not case sensitive.
Material Properties¶
F_CD |
Design compressive strength of concrete [MPa] |
F_CK |
Nominal strength of concrete [MPa] |
F_CM |
Mean value of compressive strength of concrete [MPa] |
F_CTD |
Design tensile strength of concrete [MPa] |
F_CTM |
Mean value of tensile strength of concrete [MPa] |
F_BD |
Bond strength of concrete [MPa] (DIN EN1992-1-1, 8.4.2) |
F_YK |
Characteristic yield strength of reinforcement [MPa] |
F_YD |
Design yield strength of reinforcement [MPa] |
F_TK |
Characteristic tensile strength of reinforcement [MPa] |
Section & Layer Geometry¶
SECTION_HEIGHT |
Height of section [m] |
SECTION_WIDTH |
Width of section [m] |
LAYER_ID |
Number of layer |
LAYER_ZS |
Local z-coordinate of layer [m] |
LAYER_WIDTH |
Length of layer [m] |
IS_COLUMN |
Boolean variable: 1=true, 0=false |
IS_BEAM |
Boolean variable: 1=true, 0=false |
ISLOWERREINFORCEMENT |
Boolean variable: 1=true, 0=false |
ISUPPERREINFORCEMENT |
Boolean variable: 1=true, 0=false |
ISBASEREINFORCEMENT |
Boolean variable: 1=true, 0=false |
MAXBARSTEPDIFFERENCE |
Maximum step difference between base and supplemental reinforcement diameter |
Longitudinal Reinforcement¶
ISMAINDIRECTION |
Condition for reinforcement in main direction (Boolean variable: 1=true, 0=false) |
C_ASL |
Cover of longitudinal reinforcement [m] |
D_ASL |
Diameter of longitudinal reinforcement used [m] |
D_KST |
Diameter of constructive reinforcement [m] |
D_ASL |
Diameter of base longitudinal reinforcement [m] |
D_ASL2 |
Diameter of supplemental longitudinal reinforcement [m] |
S_ASL |
Spacing of longitudinal reinforcement [m] |
S_ASL2 |
Spacing of longitudinal reinforcement [m] |
ASL_REQ_MAX |
Required maximal longitudinal reinforcement [m2] |
ASL_PRO |
Longitudinal reinforcement provided [m2] |
N_ASL |
Number of longitudinal bars |
ASL_UTIL |
Utilization factor as_req/as_pro |
F_ASL |
Factor for over-/under-reinforcement |
Shear / Transverse Reinforcement¶
ISTRANSDIRECTION |
Condition for reinforcement in transverse direction (Boolean variable: 1=true, 0=false) |
C_ST |
Cover of shear reinforcement [m] |
D_ST |
Diameter of shear reinforcement [m] |
S_ST |
Spacing of shear reinforcement [m] |
ASB_REQ_MAX |
Required shear reinforcement [m2/m] |
ASB_PRO |
Minimum shear reinforcement [m2/m] |
HOOK_ANGLE |
Angle of the hook |
HOOK_LENGTH |
Length of the hook |
F_ASB |
Factor for over-/under-reinforcement |
Anchorage of Reinforcement¶
IS_ANCHORAGE_STRAIGHT |
Boolean variable: 1=true, 0=false |
IS_ANCHORAGE_BEND_BAR |
Boolean variable: 1=true, 0=false |
IS_ANCHORAGE_HOOK |
Boolean variable: 1=true, 0=false |
IS_ANCHORAGE_WELDED |
Boolean variable: 1=true, 0=false |
ALPHA_1 |
Factor considering shape of bars |
ALPHA_2 |
Factor considering concrete minimum cover |
ALPHA_3 |
Effect of confinement by not welded transverse reinforcement |
ALPHA_4 |
Effect of confinement by welded transverse reinforcement |
ALPHA_5 |
Effect of transverse pressure |
ALPHA_6 |
Percentage of lapped bars (DIN EN1992-1-1, 8.7.3 (2)) |
LB_RQD |
Base value of development length [m] (DIN EN1992-1-1, 8.4.3 (2)) |
LB_D |
Design value of development length [m] (DIN EN1992-1-1, 8.4.4 (1)) |
LB_EQ |
Alternative development length [m] (DIN EN1992-1-1, 8.4.4 (2)) |
D_MIN |
Mandrel diameter for longitudinal bars [m] |
D_MINST |
Mandrel diameter for strirrups [m] |
L_0 |
Lap length [m] |
REINFORCEMENTINTENSION |
Boolean variable: 1=true, 0=false |
REINFORCEMENTINCOMPRESSION |
Boolean variable: 1=true, 0=false |
PERCENTAGELAPPEDBARS |
Percentage of lapped bars (Table 8.3) |
ISBONDGOOD |
Boolean variable: 1=true, 0=false |
Plates only¶
IS_FLOOR |
Boolean variable: 1=true, 0=false |
IS_WALL |
Boolean variable: 1=true, 0=false |
THICKNESS |
Thickness of Slab / wall [m] |
SOFLAYERS |
Boolean variable: 1=true, 0=false |
BASEREINFORCEMENTSYSTEM |
Boolean variable: 1=true, 0=false. Area reinforcement will be used for base reinforcement |
BAR_LEN |
Minimum valid length of rebars [m] |
AS_DIFF |
Differential As to consider a change in the reinforcement distribution [m2/m] |
MERGE_LEN |
Maximum length to merge rebar sets [m] |
MERGE_AS |
As to consider two reinforcement surfaces as able-to-merge [m2/m] |
AS_BASE |
Base reinforcement [m2/m] |
NO_BASE_REINFORCEMENT |
Create no base reinforcement, Boolean variable: 1=true, 0=false |
RECOGNIZE_REINFORCEMENT |
Consider existing reinforcement, Boolean variable: 1=true, 0=false |
Other¶
W_FACTORS |
Weighting factors used in optimization |
CONSTRAINTSFILE_ONLY |
Boolean variable: 1=true, 0=false. Ignore dialog input |
CREATESINGLEBARS |
Boolean variable: 1=true, 0=false. Create single bars (no rebar sets) |
APPLYMATCHINGXFORM |
Boolean variable: 1=true, 0=false. Compare exported geometry with Revit geometry to create bars in the Revit location (CDB only) |
ADSJUSTTOSECTION |
Boolean variable: 1=true, 0=false. Adjust parametrically the reinforcement to the Revit geometry in case it is distinct to the exported model(CDB only) |
Anchorage¶
The determination of anchorage and laps can be controlled by design rules. The anchorage development length is defined by the parameter “LB_D”, the engineer can modify the constraints file and influence on its calculation.
In the default constraint file, the anchorage length in defined according the Eurocode EN 1992-1-1:2004 as follows:
//$ --------------------------------------------------------------------
//$ 8.4 Anchorage of longitudinal reinforcement
//$ --------------------------------------------------------------------
//$ 8.4.2 Ultimate bond stress
f_bd = 2.25*eta_1*eta_2*f_ctd
//$ 8.4.2. Bond conditions
eta_1 = 0.7 ; isBondGood : eta_1 = 1.0
eta_2 = 1.0 ; d_asl > 0.032 : eta_2 = (0.132-d_asl)*10
//$ 8.4.4 Design anchorage length
lb_d = alpha_1*alpha_2*alpha_3*alpha_4*alpha_5 * lb_rqd * asl_util
//$ 8.4.4 (1) Minimum anchorage length
reinforcementInTension : lb_d >= MAX(0.3*alpha_1*alpha_4*lb_rqd,10*d_asl)
reinforcementInCompression : lb_d >= MAX(0.6*lb_rqd,10*d_asl)
//$ 8.4.4 (2) alternative anchorage length
lb_eq = 0.7 * lb_rqd * asl_util
//$ Coefficients of Table 8.2
alpha_1 = 1.0 //$ factor considering shape of bars
alpha_2 = 1.0 //$ factor considering concrete minimum cover
alpha_3 = 1.0 //$ effect of confinement by not welded transverse reinforcement
alpha_4 = 1.0 //$ effect of confinement by welded transverse reinforcement
alpha_5 = 1.0 //$ effect of transverse pressure
The anchorage length is considered for the visualization of the reinforcement as an offset on the inserted reinforcement range measured since the beginning/end of the bars. Below the anchorage length is highlighted green next to the boundary of the reinforcement distribution diagram.